What is the diameter of the rod to choose for an external metric thread? Internal threading Manual internal threading sequence

Instructions

A thread is essentially a helical groove cut into an outer or inner cylindrical surface. It is mainly used to connect various parts to each other. In mechanical engineering, it can be used to convert translational motion into rotary motion and vice versa. There are two types of threads, metric 60o and pipe 55o.
In metric, diameter and thread pitch are measured in millimeters. When designating metric threads, alphabetic and numeric are used, for example M8x1.5. The number eight corresponds to the thread diameter, and 1.5 means the thread pitch, in turns.
In inch threads, measurements are in inches and numbers per inch. One inch equals 2.54 cm. For example, an inch is written 1 1/4 ".

To cut an external thread, you need to take a die the right size and prepare a workpiece, and in particular, select a workpiece of a certain diameter. The diameter of the workpiece for threading is determined from the tables. In practice, for cutting, for example, a thread with a diameter of M6, a rod with a cross section of 5.92 mm is required, that is, approximately one tenth of a millimeter less; for an M8 thread, the workpiece must have a diameter of 7.9 mm.
For example, here is an extract from the table of bar diameters under metric thread:

Thread diameter / rod diameter (mm) - 5 / 4.92; 6 / 5.92; 8 / 7.9; 10 / 9.9; 12 / 11.88; 16 / 15.88; 20 / 19.86; 24 / 23.86
After the selection of the workpiece, it is clamped in a vice, the chamfer is removed from the end with a file, for the correct entry of the die, and the thread is cut with rotary-clamping movements, not forgetting to lubricate the part with machine oil.

The internal thread is cut with a tap. Preliminary drilled holes should be the smaller diameter of the thread you need. Extract from the table drill diameters for drilling holes is shown below.

Thread diameter / hole diameter (mm) - 2 / 1.6; 3 / 2.5; 4 / 3.3; 5 / 4.2; 6 / 5.0; 8 / 6.7; 10 / 8.4; 12 / 10.2; 16 / 13.9; 20 / 17.4; 24 / 20.9
To cut a thread inside the part, you must have two taps, rough and finish.

We also clamp the part into the test piece and, with rotational movements with a slight pressure, cut the thread with a rough tap, periodically lubricating the tap with machine oil, then make a finishing pass. The thread is ready for use.

note

For better threads, rotate the knob 180 ° clockwise and then 90 ° counterclockwise. This cuts long chips and reduces the force on the wrench.

Sources:

how to tap a thread

Many years ago, when the era of fasteners was just beginning, making a nut was a task that only a highly skilled craftsman could do. Slicing today internal thread is a routine operation. Nevertheless, for its high-quality implementation, you need to have certain knowledge and skills.

You will need

Electric drill, set of drills and taps, thread gauge, vernier caliper, metric thread size table.

Instructions

Decide on the parameters of the thread to be cut There are many types of threads, but most often we have to deal with metric threads, which are characterized by two parameters - diameter and pitch. If there is a bolt for which you want to cut the inner one, measure its parameters. The thread diameter is measured with a vernier caliper, the pitch is measured with a thread gauge. If there is no thread gauge, the thread pitch can be measured in the following way. Press the threaded bolt against a clean piece of paper and roll it around so that the thread is imprinted on the sheet. Count how many turns are in a given length and divide that length by the number of turns. The resulting value will be the approximate thread pitch. Select the nearest standard pitch from the metric thread size table.

Determine the diameter and depth of the hole that needs to be made for threading To determine the diameter, use the same table that was used to determine the standard pitch. The required parameter is usually denoted d1 or D1. If the thread is tapped in a blind hole, it is necessary to determine the drilling depth of the hole. She must be more depth tapping by a certain amount, which depends on the design of the tap. Measure the length of the cutting (intake) part of the tap and add it to the required thread depth. This will be the required hole drilling depth.

Drill a hole of the desired diameter to the required depth If the diameter of the existing drill does not match the hole diameter found in the table, use the closest drill bit. However, keep in mind that the difference between drill diameter and standard hole size should not be significant compared to thread pitch. After drilling the hole, make a small chamfer in it with a larger diameter drill.

To do this, fix the tap in the knob, insert it into the hole and, with force pressing the tap to the hole, give it a rotational motion. At the same time, try to maintain the perpendicular position of the tap in relation to the surface of the part. When the tap is firmly embedded in the hole, you can limit yourself to one rotational motion.

Thread types

They differ in their main characteristics:

system of calculating diameter (inch, metric, others);
the number of visits (two-, three- or one-way);
profile shape (rectangular, trapezoidal, triangular, round);
direction of rotation of the screw (left or right);
placement on parts (internal or external);
part shape (cone or cylinder);
purpose (running, fastening and sealing or fastening).

According to the listed characteristics, the following types are distinguished:

cylindrical (MJ);
metric and conical (M, MK);
pipe (G, R);
Edison's round (E);
trapezoidal (Tr);
round for plumbing fixtures (Kp);
persistent (S, S45);
inch, including cylindrical and conical (BSW, UTS, NPT);
oil assortment.

Internal threading tools

To make internal cuts, you need a tap - a screw-shaped tool with sharp flutes. The rod can be in the form of a cone or a cylinder. The grooves go along and break the threads into sections called combs. It is the edges of the combs that are the working surfaces.

To make the groove clean, the metal is removed gradually, in layers. This requires one very long tool or set.

Single taps are also available on the market, and are more commonly used to fix stripped threads. To cut a new one, they buy a kit. Therefore, taps are usually sold in pairs: for roughing and for finishing work... The first cuts a shallow groove, the second cleans and deepens it. There are also three-pass instruments. Thin taps, up to 3 millimeters, are sold in two, wider - in three. Three-way taps are inserted into the driver. The device of the cranks is different, but their size must match the size of the cutter.

In a set, tools are distinguished by the risks applied to the tail end. If you look closely, you can see the shape differences:

the first tap with heavily cut tops of the teeth, the outer diameter is slightly smaller than the other tools in the set;
a second tap with a shorter intake segment, longer flanges. Its diameter is slightly larger than that of the first;
the third tap has full ridges of teeth, and its diameter must match the dimensions of the future thread.

Taps are divided into pipe (marked with "G") for threading inside the pipe and metric - the more common.

The quality directly depends on the properties of the tap: it must be made of good metal and sharp. To prolong the life of the tool and improve the quality of the threads, a lubricant is used. Usually, it takes 3 - 5 attempts to acquire a stable cutting skill.

Slicing process

Before you start cutting, you should make a hole in the workpiece with the help of drills. The diameter of the hole from the drill must match inner dimension carving. When the size of the hole made by the drills is selected incorrectly, the tool can break or the grooves will turn out to be of poor quality.

During cutting, part of the metal does not fall out with chips, but is pushed along the working surfaces of the tap, forming a groove profile on the workpiece. Given this feature, the size of the drill, which makes the hole for the thread, is selected slightly less than the nominal diameter of the future thread.

For example, when cutting M5 (groove diameter is 5 mm), you should choose a drill for a 4.2 mm hole. To cut M4, the drill diameter should be 3.3 millimeters, and before working with the M6 tap, a hole is pre-drilled with a 5 mm drill. This indicator is calculated taking into account the thread pitch. The step can be calculated mathematically, but in practice they resort to correspondence tables, where for the M5 tap the step is 0.8, for the M4 this indicator is 0.7, for the M6 - 1. Subtract the step indicator from the diameter and get required diameter drill. When working with brittle metals such as cast iron, the drill diameter should be reduced by 0.1 mm from the recommended size in the table.

The formula for calculating the hole diameter when working with three-way taps:

Up = Dm * 0.8;

here: Dm - tap diameter.

Type of	Diameter	Step
M1	0,75	0,25
M1.2	0,95	0,25
1,4	1,1	0,3
1,7	1,3	0,36
2,6	1,6	0,4
2,8	1,9	0,4
M3	2,1	0,46
M3	2,5	0,5
М4	3,3	0,7
M5	4,1	0,8
M6	4,9	1
М8	6,7	1,25
M10	8,4	1,5

Table 1. Correspondence of thread diameters and preparation hole

Before starting work, the tap is inserted into a square shank - a knob. The gates can be conventional or with a ratchet. The thread is done carefully, the first pass is made with a tap number 1 to the end. Particular attention must be paid to the direction of movement: only clockwise, while it is necessary to apply some effort. It is carried out as follows: 1 \ 2 of a turn along the way alternates with 1 \ 4 of a turn against the screw to break the chips.

Thread in inches	Outer D, mm	Diameter, mm	Step, mm
1 \ 8 ″	2,095	0,74	1,058
1 \ 4 ″	6,35	4,72	1,27
3 \ 16 ″	4,762	3,47	1,058
5 \ 16 ″	7,938	6,13	1,411
7 \ 16 ″	11,112	8,79	1,814
3 \ 8 ″	9,525	7,49	1,588

Table 2. Bore diameters for inch threads

A couple of drops of grease make it much easier to work on blind threaded holes. Although machine oil is sometimes used as a lubricant, drying oil is optimal for working with steel. With aluminum alloys, it is preferable to use kerosene, alcohol or turpentine. Technical oil can also be used, but with less effect.

Homemade tap for aluminum alloys

To create internal threads in brass or alloy parts, you can use homemade tool and drills from the usual set. Calibrated steel wire will do. With the help of a die, an external thread is cut on it, after which the workpiece is hardened. After hardening, it is necessary to release the part to the color of ripe straw. The cutting edges are sharpened with a bar or sharpener, after clamping the part in a collet chuck.

Video on how to cut an internal thread:

The question of how to tap a thread arises when a pre-drilled hole must be prepared to accommodate a bolt, screw, stud, and any other type of threaded fastener. It is the tap in such situations that is the main tool that allows you to quickly and accurately cut an internal thread with the required geometric parameters.

Varieties and scopes of taps

Internal threading can be done manually or using machine tools different types(drilling, turning, etc.). Working tools that perform the main work on cutting internal threads are machine-hand or machine taps.

On different kinds taps are divided depending on a number of parameters. The following principles for the classification of taps are generally accepted.

According to the method of rotation, machine-hand and machine taps are distinguished, with the help of which the internal thread is cut. Machine-hand taps equipped with a square shank are used in a set with a special device with two handles (this is the so-called wrench, tap holder). With the help of such a device, the tap is rotated and cuts the thread. Threading with a machine-type tap is carried out on metal-cutting machines of various types, in the chuck of which such a tool is fixed.
By the way in which the internal thread is cut, there are universal (through) and complete taps. The working part of the former is divided into several sections, each of which differs from the others in its geometrical parameters. The section of the working part, which first begins to interact with the machined surface, performs roughing, the second - intermediate, and the third, located closer to the shank, - finishing. Complete taps require multiple tools to thread. So, if the set consists of three taps, then the first of them is intended for roughing, the second for intermediate, and the third for finishing. As a rule, a set of taps for cutting threads of a certain diameter includes three tools, but in some cases, when products made of special solid material, sets of five instruments can be used.
By the type of hole, on the inner surface of which it is necessary to cut a thread, taps are distinguished for through and blind holes. The through-hole tool is characterized by an elongated tapered tip (lead-in) that merges smoothly into the working end. This design is most often used by universal type taps. The process of tapping internal threads in blind holes is carried out with taps, the tapered tip of which is cut off and performs the function of a simple cutter. This design of the tap allows you to use it to cut threads to the full depth of the blind hole. For threading of this type, as a rule, a set of taps is used, which are manually rotated using a wrench.
According to the design of the working part, the taps can be with straight, screw or shortened chip-removing grooves. It should be borne in mind that taps with different types of grooves can be used for threading in products from relatively soft materials- carbon, low-alloy steel alloys, etc. If the thread needs to be cut in parts made of very hard or viscous materials (stainless, heat-resistant steels, etc.), then taps are used for these purposes, the cutting elements of which are staggered.

Taps are usually used for cutting metric threads, but there are tools with which to cut pipe and inch female threads. In addition, taps differ in their shape. work surface, which can be cylindrical or conical.

Preparing for internal threading

In order for the process of cutting internal threads with a tap to not cause any particular difficulties and end with a high-quality result, it is necessary to properly prepare for this technological operation. All tapping methods assume that a hole with the appropriate diameter has already been made in the workpiece. If the internal thread to be cut has standard size, then a special table with data according to GOST can be used to determine the diameter of the preparation hole.

Table 1. Diameters of holes drilled for standard metric threads

In the event that the thread that needs to be cut does not belong to the standard category, you can calculate the hole diameter for its implementation using the universal formula. First of all, it is necessary to study the marking of the tap, in which in mandatory indicates the type of thread to be cut, its diameter and pitch, measured in millimeters (for metric). Then, to determine the size cross section the hole that must be drilled for the thread is enough to subtract the pitch from its diameter. For example, if a tool marked M6x0.75 will be used to cut a non-standard internal thread, then the diameter of the preparation hole is calculated as follows: 6 - 0.75 = 5.25 mm.

For standard threads belonging to the inch category, there is also a table that allows you to choose the right drill with which preparatory work is performed.

Table 2. Diameters of holes drilled for an inch thread

An important question for obtaining a high-quality result is the question not only of what the thread is cut with, but also of which drill to make the preparatory hole. When choosing a drill, it is necessary to pay attention to the parameters and quality of its sharpening, as well as to the fact that it rotates in the chuck of the equipment used without beating.

The sharpening angle of the cutting part is selected depending on the hardness of the material to be drilled. The higher the hardness of the material, the larger the sharpening angle of the drill should be, but this value should not exceed 140 °.

How to cut the threads correctly? First you need to pick up tools and consumables:

an electric drill or drilling machine capable of operating at low speeds;
drill, the diameter of which is calculated or selected according to reference tables;
a drill or countersink, with the help of which a chamfer will be removed from the edge of the prepared hole;
a set of taps of the appropriate size;
manual holder for taps (knob);
locksmith's vice (if the product, in which it is necessary to cut the thread, must be fixed);
core;
hammer;
machine oil or other compound, with which during processing it is necessary to lubricate both the tap and the section of the thread cut by it;
rags.

Technology features

When tapping an internal thread, the following algorithm is followed.

In the place on the surface of the workpiece where the hole for threading will be drilled, it is necessary to form a recess for a more accurate drill entry using a core and a conventional hammer. The drill is fixed in the chuck of an electric drill or drilling machine, at which low rotation speed of the tool is set. Before starting drilling cutting part drills must be treated with a lubricating compound: the lubricated tool is easier to enter into the structure of the material being processed and creates less friction in the processing area. You can lubricate the drill with a piece of ordinary lard or grease, and when processing viscous materials, machine oil is used for these purposes.
If threading is necessary in detail small size, they should be pre-fixed using a bench vice. Starting drilling, the tool, fixed in the chuck of the equipment, must be positioned strictly perpendicular to the surface of the workpiece. The tap should be lubricated regularly and ensured that it does not tilt and moves strictly in the specified direction.
At the entrance to the hole made, as mentioned above, it is necessary to remove a chamfer, the depth of which should be 0.5–1 mm (depending on the diameter of the hole). For this purpose, a larger diameter drill or a countersink can be used by installing them in the chuck of the drilling equipment.
The internal threading process begins with the # 1 tap, which is the first to be inserted into the driver. Do not forget about the lubricant, which must be applied to the tap for threading. The position of the tap relative to the hole to be machined must be set at the very beginning of work, since then, when the tool is already inside the hole, this will not work. When tapping with a tap, you must adhere to the following rule: 2 turns of the tap are made in the course of threading, 1 - against the course. When the tap is made one turn backward, chips are thrown off the cutting end and the load on it is reduced. Die cutting is performed in a similar manner.
Having cut the thread with a tap No. 1, tool No. 2 is installed in the knob, and after it - No. 3. Their processing is carried out according to the above described method. When tapping with taps and dies, you need to feel when the tool starts to rotate with effort. As soon as such a moment comes, you should turn the knob in reverse side to dump chips from the cutting edge of the tool.

— actual question since this is the main method for connecting structural elements.

This can be done manually using a special device.

Separate the external and internal cutting of the part, thanks to which the thread can be installed in a hole of different types.

The cutting method depends on the type of material you will be working with.

Features of the process, as well as a description of the tools that are needed for this, you will find in the article, and the video will help you cope with the task.

Slicing tap

A tap is called a metalwork-turning cutting device made in the form of a rod with a cutting element installed on it.

The cutter is used to create internal threads in various metal parts, pipes, and it can also be used to restore previously damaged threads.

The cutter has a working and tail... The working part includes two sections: for cutting and for calibration.

The cutting area is usually tapered and is responsible for direct threading.

Cutting teeth are also installed in this area, which cover the area around the entire circumference. The sizing area is responsible for the final shaping of the part.

It looks like a toothed cylinder and continues the cutting area.

It is longer, and its working element is divided by the grooves necessary to create cutters and remove chips.

The number of grooves depends on the size of the die with a die - in devices not exceeding 22 mm, there are usually three of them. There are also special taps in which there are no grooves.

In those devices where they are, the grooves can be straight or helical.

The back of the tap has a cylindrical shape, at the end of it there is a square, which is necessary to be able to fix it to the fastening tool.

This part of the tap is responsible for attaching the device to the hand holder or chuck of the machine tool.

There are two types of die taps: manual or machine. Handheld devices attach to hand-held holders and are designed to create internal threads.

Machine tools are mounted on chuck holders of lathes.

Before you know how to tap a thread, you need to decide on its type. The threads that can be made vary depending on the type of device.

The most common form of thread is metric - it is made using a metric tool.

To create threads on the inside water pipe, as well as in the heating pipe, they use specialized pipe taps, they can also make reinforced threads in metal parts, and not only in heating elements.

To create a tapered or inch thread, you need to use a special inch tap, which allows you to make the smallest thread.

Most often, you can find strong steel devices with a die - they are the most effective, strong and durable.

In addition to the type of thread, taps differ in design: they can be single or complete.

The latter are used to create threads in several passes. Typically, the kit includes two taps, one of which is called finishing, and the other is rough.

In some cases, a medium tap is added here. The number of parts in the kit is always indicated on the back, on the part of the tail.

Complete taps are not the same, they have different shapes teeth: the rough one has the shape of a trapezoid tooth, the middle one is triangular, the apex of which is rounded, and the finishing one is a standard triangle with a sharp apex.

Tapping is to create a protrusion in a hole, with the line of the protrusion having a helical shape.

The protrusion near the wall in the hole must match the specified parameters in order for the thread to be used: it must have the correct pitch, lifting angle, outer and inner diameters, etc.

Also important parameter is the depth, which is determined based on the diameter of the threads inside and outside on the pipe.

There may be several options for how to properly cut the thread.

The direction of the thread in the pipe can be different, depending on the need: it can be directed to the right, while the protrusion develops clockwise, or has a left direction, then the protrusion will follow counterclockwise.

There are two possible profile shapes: rectangular or triangular, as well as special additional shapes, but they are used mainly in production, and almost never at home.

Tap selection and cutting

A tap is chosen depending on the thread that is needed, as well as its purpose (the thread may differ in profile shape, thread pitch, tolerances).

To select a tap, there is a table that reflects the accuracy classes - in accordance with them, you need to choose which type of tap to purchase - a set, or a single tool.

An important factor to consider when choosing a tap is the required profile cutting accuracy.

Different instruments have different purity processing of the cutting element, and this must also be taken into account.

The metal you will be working with directly affects the tap that you need for this.

On aluminum, a sharpening angle of at least 25 degrees is required, up to 5 degrees on cast iron and copper, and up to 10 degrees on steel.

For the manufacture of the tap itself, most often ordinary or high-strength steel is used. When choosing, you need to focus on the diameter in the hole in which the thread will be made.

Before you can create a thread in aluminum, cast iron, or any other metal part, you need to make a hole. It can be through or deaf, depending on the need.

The hole can be of any diameter, it is only important that it is smaller than the future cut. The drill for the hole is best selected based on the size of the thread.

There is a special table that reflects the recommended drill diameter in accordance with the thread size, it is recommended that you familiarize yourself with it before starting work.

If you need to make a large wall thread on cast iron or aluminum, then you should choose the diameter for the hole by multiplying the thread diameter by 0.8, so you get the value that will be the maximum near the required size.

The creation of a hole for an internal thread is not given manually, but using a special drilling machine, or an electric drill.

In the case of using a drill, the workpiece must first be clamped in a vice so that the drilling site is exactly where it is needed.

When drilling, the drill must be positioned strictly vertically and not deviate from the specified plane.

To make the tap easier, you can chamfer the top edge to make it easier to fit in.

This can be done using a drill with a larger diameter, or a file. After finishing work, the hole must be cleaned of chips.

Especially carefully you need to do this in a blind hole, otherwise you will not be able to cut it qualitatively.

Before drilling, the part you will be working with must be tightly fastened with a vise, with the chamfer on top, and the axis of the hole you made should be perpendicular to the table.

The tap must be fixed in the socket of the driver, and then inserted into the chamfer of the blank hole. The device is always inserted vertically.

After that, the tap must be strongly pressed against the workpiece (preferably with both hands) and begin to rotate it clockwise.

Do not allow sudden movements or stops: you need to rotate the device slowly and evenly, but at the same time work with pressure.

You need to work with a tap in the following sequence: first two turns forward, then half a turn back and then again forward. This method is used to process the entire hole in the pipe.

The tap needs to be cooled from time to time during cutting.

For different metals are used different ways cooling: kerosene will be effective for aluminum, turpentine for copper, for other metals - a special emulsion, and when cutting in cast iron, cooling of the device is not required.

For internal cutting it is best to use tap kits.

The work is as follows: first you need to make a rough thread, then use the middle tap, which is passed through the hole, and then the final cut is formed using a finishing tap.

This sequence is optimal for best quality processing, therefore it is recommended not to skip any of the three devices, otherwise the quality of the thread in the pipe will be noticeably worse.

You can see all the stages of the cutting process in the video - there is nothing complicated in this process, the most important thing is to choose the right diameter and follow the sequence of work, as well as remember how to work with this or that type of metal.

In this case, you will receive a high-quality pipe thread that can be used to connect any parts.

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Often at runtime home renovation it becomes necessary to make a thread - external or internal. In order not to involve specialists in this, but to do it yourself, you need to purchase a special tool. Cutting with dies and taps does not require special skills or abilities. It is enough to know their types and technical parameters.

A little about the features of the tool

At the first stage, you should decide on the type of thread. It is divided into 2 main types: metric and imperial. The first one with the left direction is most often used. In order not to measure the distance between the grooves, you can recognize the type by the shape. The metric thread in the cross section is an equilateral triangle, and the inch is isosceles.

What products use a particular thread type? Fasteners use metric and plumbing uses inch. In addition, the following factors must be taken into account that affect the performance of the cutting process of connecting elements.

If the thread is intended to be connected to an already finished part, its geometric dimensions must be appropriate.
In the manufacture of fasteners completely - it is recommended to use the metric type.
The diameter of the workpiece must be different from the thread size. For the outside - in the smaller direction, for the inside - in the larger one.

Self-cutting threaded connections performed using dies and taps. They are made of high-strength steel with a standardized size of the working fluid.

Outdoor

The die is a nut with internal slots and external locks for turning the tool. It can be of various shapes - round, square or hexagonal. If the work is carried out at home, you will need a vice to fix the part.

Before doing the work, the main thing is to choose the right diameter of the workpiece. It should be 0.2-0.3 mm smaller than the size of the future thread. For metric, you can use the data from the table.

The workpiece must be prepared in advance. If its section is not a circle, you need to turn it. Then a tapered chamfer is removed on the end part to mark the first thread.

Having fastened the workpiece in a vice, the correctness of its location is checked.
Installing the die into the die holder. Its surface should be in the same plane with the surface of the end face of the workpiece.
The first turn is done with little effort. It is important to make turns in the right direction.
Having reached the bottom border, the die must be turned in the opposite direction.

One such pass will not be enough to form a thread with good geometry. It is recommended to repeat the procedure 3-4 times until the die is free to twist onto the workpiece. To check the quality, a nut of the appropriate diameter should be tightened. If force is observed, the outer part of the workpiece can be machined sandpaper fine grain.

Internal

Taps must be used to form internal threads. They represent a cylinder with an external groove. If it is necessary to process small parts with a diameter of up to 20 mm - you can use manual view tap. For large sizes is necessary mechanical restoration using .

It is best to use a complete set of taps. It includes three parts for roughing, intermediate and final shaping. threaded holes... If in home recruitment there is a drill - it is recommended to purchase taps with a tail mount.

The workpiece must be secured. If this is a large-sized part, this can be done using clamps. For small products, a vice is used. Having secured the part, its position relative to the tap is checked. The axis of the latter must be strictly perpendicular to the plane of the workpiece. The first pass will be done with great effort. Do not forget that for this you need to use a tap for rough handling... Having formed the primary thread, a tap is used for the intermediate one. And only after it you can proceed to the final processing.

To reduce friction, specialists use grease or a similar agent. In this way, mechanical damage to the part can be avoided. The formed thread must have the same geometry along its entire length. Otherwise, loss of strength of the connection is possible.