How to measure thread pitch with a caliper?

Metric fasteners are specified in thread pitch instead of thread count. The thread pitch is the distance between them. Thread is expressed in millimeters (measured along the length of the fastener). For example, a thread pitch of 1.5 means that the distance between one thread and the next is 1.5 mm. Smaller fasteners have finer threads, so they have smaller thread pitches.

Measuring the thread pitch is carried out as follows: using a ruler or caliper, measure a section of the required size on the rod. Then count the number of turns in the measured area. The recommended length of the section to obtain an accurate measurement is 20 mm.

Measuring with a thread gauge

Accurately identifying the threads on a fastener is critical before selecting and installing the correct fittings.

How to measure thread:

1. Use a combination caliper to measure the thread diameter. It is worth taking into account that the threads of the used fitting may wear out and become distorted, so calculations may not be accurate.
2. Use a thread gauge to determine the number of threads per inch. For metric connections, the distance between the threads is calculated. To do this, you need to place the device on the thread until it fits snugly, and then compare your measurements with the thread diagram.
3. If the port is located at an angle, determine the angle of inclination using a protractor on the sealing surface. The center line of the fitting and gauge should be parallel.

Using a combination of three tools, identifying connectors is easy. The use of a caliper, thread gauge and protractor allows accurate measurements of most connections.

To calculate the thread pitch - the distance between the turns of the threads, you need to measure the threaded element with a ruler or caliper and count the number of turns in this area. Dividing the length by the number of turns gives the thread pitch. The value of the indicator is expressed in millimeters.

The distance between the turns of the threads can be measured with a caliper or thread gauge. Less accurate results are obtained by measuring a section of the rod with a ruler, counting the number of turns, and dividing the length by the number of threads. The indicator is calculated in millimeters. The thread pitch is indicated in the technical documentation and in the part markings.

A caliper is used to measure the diameter of an external internal thread. When comparing calibration measurements to thread diagrams, keep in mind that threads on connections that have been in service may be worn and distorted from use. This results in inaccurate comparisons with thread tables.

This is a more accurate way to measure thread pitch. A caliper is used to measure a section of a certain length. Then count the number of turns on it. The thread pitch value is obtained by dividing the length of the section by the number of turns, and subtracting one turn from the result.

For English, British and other European threads, the pitch meter has an inch scale. However, for metric parts, the device will determine the distance between threads in millimeters.

The protractor is used by placing it on the sealing surface. The center line of the fitting end and gauge should be parallel. In English, the thread size system and pitch (number of threads per inch) are specified along with the thread type.

When using a thread gauge, you need to align it with the threads and make sure that it fits snugly. Match the measurement to the thread, then calculate the diameter using a caliper.

Internal connections are measured by inserting the identification part of the device into the connector on the sealing surface. Make sure that the center lines of the connection and the protractor are parallel. This will allow you to determine the correct angle.

It is necessary to measure a certain length of a section of the rod with a caliper or by applying a ruler to the surface. Count the number of turns in this area. It is recommended to carry out the calculation on a length of 20 mm or 10 mm. The thread pitch is obtained by dividing the length by the number of turns.

Using the above methods, you can measure the thread pitch of any fastener. This can be either a nut with a flange and a locking plastic insert, or a washer with an internal cone.

Measuring the internal diameter of a thread

The internal diameter of the cutting is controlled by a measuring device with pointed legs - calipers.
To organize computational work, you need to install the tool on a template part using a threaded gauge, and then make a comparison with the original internal diameter of the threaded connections. The caliper must be at an angle relative to the axis being measured. Also, measuring internal threads can be carried out with instruments for cylindrical threads. This is because the inside diameter has a smooth surface, which is ideal for the shape of the tips used in these instruments. Verification of the obtained measurements is done using plug gauges.

Measuring thread pitch without a thread gauge

For metric fasteners, thread pitch is used instead of TPI. Distance is also measured in millimeters.

The distance between the vertices of the threaded profile of a nut is called the thread pitch. To obtain accurate results, use a caliper or thread gauge. A rough calculation can be made using a ruler - by measuring the length of a given section and counting the number of turns without taking into account the first. Divide the length of the segment by the number of turns to get the thread pitch of the nut.

To determine the thread pitch, a caliper is used to calculate the distance from the top of one thread to the next. The formula used for this is M2 x 4 x 5 mm, where M2 refers to the diameter of the bolt (in millimeters), i.e. 4 is the thread pitch in millimeters, which means it is equal to 4 mm between each thread peak, and 5M is bolt length.

Thread pitch is used to measure the threads of a bolt or nut to ensure they fit together. If the threads of the bolt and nut are different, they either do not grip or wear out the threads, resulting in an unusable connection.

Small threaded fasteners have a denser helical structure and are usually less pronounced. A coarse threaded connection has larger and deeper threads. This means that if the threads are slightly damaged, it may still work. Most standard metric fasteners have fine and coarse threads. Each of them can be identified using or thread pitch.

To accurately determine the thread pitch by diameter, use a caliper. The measurement result is obtained in millimeters. Measurement accuracy up to tenths of a millimeter. Compare with the indicators of a standardized table of diameters, which indicates the correspondence of the thread pitch to each diameter.

In the US and UK, fasteners typically have thread sizes ranging from ¼ to 20 inches and ¼ to 28 inches. To determine which of these threads is coarse and which is fine, you simply need to take the TPI number (20 and 28) and compare them.

Don't forget that coarse thread means the thread is larger, so smaller ones will be able to fit within an inch. So 20 means it's a coarse thread and 28 means it's a fine thread. TPI and thread pitch will vary depending on the diameter of the fastener, so the value will not always be 20 and 28.

For metric fasteners, similar parameters would be represented as M8 x 1.25 or M8 x 1. For thread pitch, the distance between two points is the second number, meaning the higher the number, the fewer threads. It follows that M8 x 1.25 is a coarse thread, and M8 x 1 is a fine thread.

The most accurate and fastest way to determine the thread pitch is using a caliper. This tool is used to measure the length of the desired section and count the number of turns located on it. Next, the resulting length is divided by the number of threads, and one turn is subtracted from the result.

Average diameter of threaded connection

To determine the average diameter of a thread, you need a micrometer with special tips in the form of a cone and a cutout. It is used to determine the size of the part at the top of the thread and at the root to calculate the average value. When selecting a kit, it is necessary to take into account the measurement limit, which is indicated in the marking with the letter M and numbers indicating the minimum and maximum allowable thread pitch. Also, to obtain the average thread value, calipers with ball tips are used, the profile of which matches the type and pitch of the thread. The tips are calibrated on several sides of the part for the most accurate result.

Measuring threads with a caliper

Accurate measurements of the thread pitch can be performed using a caliper, thread gauge, or inclinometer. This indicator can be determined by the diameter of the bolt, measuring it with a caliper and comparing the results with the indicators of a special table of metric thread pitches.

The first step is to determine whether the threads are tapering. To do this, place the points of the caliper on either side of the object that needs to be measured. Align it to the outside of the threads at the lower end, away from the head. This is how the width is determined.

The thread pitch of the fastener is determined by dividing the length of the rod by the number of protruding elements. The length is measured with a ruler or caliper if you want to get an accurate result. A ruler is applied to the upper parts of the threaded elements. The recommended length for counting turns is 20 mm.

Next, you need to move the tip so that it touches the threads. The measurement should appear on the screen if the instrument has a display. Otherwise, you will need to rely on the numbers on the sliding part. You should then do the same on the threaded area near the head of the fastener. If the number is higher at the head, then it is a tapered thread.

You can also use a caliper to measure the diameter. If the thread is tapered, measure at the 4th or 5th thread down from the head, i.e. in the middle of the threaded area. If it does not taper, then you can measure anywhere along the thread. When using a caliper, you may notice that there are several places where the arms do not meet closely together, sometimes along the edge of the ruler. There is no need to place what needs to be measured in these spaces.

The numbers should be placed in a standard measurement. Once the pitch value is obtained, you can measure the length of the bolt or screw from under the head and place all the numbers into a standard measurement. It will have the diameter, then the thread pitch and the length. If a metric screw has a diameter of 4 millimeters, a thread pitch of 0.4 mm and a length of 8 mm, then the calculation will be M4 x 0.4 x 8M. For an American screw this could be 1/4" in diameter, 20 TPI and 1" long. The formula will be: 1/4 inch x 20 x 1 inch.

The thread pitch can be determined using a ruler. This is not the most reliable, but accessible method. Use a ruler to measure the length of the desired threaded section. Then the number of threads is counted at this distance. The thread pitch value is calculated by dividing the length of the section by the number of turns.

How to measure a nut

Most nuts have metric threads. Measuring the thread diameter will require a little more steps than in other cases. If possible, it is recommended to check the size of the bolt or screw used for it rather than the nut itself. This way you can achieve a more accurate result.

The value obtained after measuring the internal thread is an indicator of the internal diameter din.

In order to accurately determine the diameter of the metric thread of the hardware, you will need to find out the correspondence between din and the outer diameter of the bolt used. This is done using a special table.

Accuracy is controlled through the use of certain pass-fail gauges. One part should connect well with the nut, the second part, on the contrary, should not.

The nuts differ in appearance, and it is easy to determine upon detailed inspection. To find out the standard of the fastener, you may need to measure the height of the hardware, since there are high, low, extra high and other options.

Turnkey dimensions are also used to classify hex nuts. This is explained by the fact that hardware also differs in its types.

To accurately measure the thread pitch, it is possible to use the method considered in the case of a bolt. You will need a thread gauge or you will have to count the number of turns at the required interval.

Determining the dimensions of inch nuts

To check the thread dimensions of an inch nut, you need to examine the threads of the bolt or other hardware used with it. If you don’t have a suitable one at hand, but have information about the presence of an inch thread, then use the appropriate thread gauge. Do not forget to divide the resulting value by 25.4 mm.

Determining washer dimensions

For washers, a short designation in the form D is used, which stands for the diameter of the metric thread of the hardware used for the fastener.

To accurately measure indicators, a ruler or caliper is suitable. The result is a value that is slightly higher than the figure in the notation. This is explained by the fact that free movement is required during installation, which requires a small gap.

So, you have a bolt or nut with unknown thread parameters, and there is no measuring tool at hand other than a ruler. Let us immediately warn you that using a ruler can only get a rough result, so if you are going to regularly take such measurements, it is better to purchase a thread gauge or caliper.

Measuring rivets

Rivets are a kind of fasteners consisting of two parts: a head and a mandrel. The cap is the short side that needs to be measured for its length and diameter. The mandrel is the long, thin end that comes off the rivet during the installation process.

First of all, you need to place the head into the round holes on a special rivet gauge. The holes have different diameters into which rivets fit. When they are inserted into the hole, the cap should fit snugly.

If there is a gap, the size is too large for the rivet. In the opposite situation it is too small. Using the selection method, you need to determine which size most accurately reflects the parameters of the fastener.

Next you need to measure the length of the rivet. To do this, you need to attach the cap to the open upper areas. Make sure that the washer or flange of the rivet is pressed well.

Accuracy classes and marking rules

A thread belonging to the inch type, as indicated by GOST, can correspond to one of three accuracy classes - 1, 2 and 3. Next to the number indicating the accuracy class, put the letters “A” (external) or “B” (internal). The full designations of thread accuracy classes, depending on its type, look like 1A, 2A and 3A (for external) and 1B, 2B and 3B (for internal). It should be borne in mind that class 1 corresponds to the coarsest threads, and class 3 corresponds to the most precise threads, the dimensions of which are subject to very stringent requirements.

Maximum size deviations according to GOST

To understand what parameters a specific threaded element corresponds to, it is enough to understand the designation of the thread that is applied to it. The designation in question is used by many foreign manufacturers who work according to American standards relating to elements of threaded connections.

An example of a symbol for an inch thread

This marking contains the following information about the thread:

• nominal size (outer diameter) – first digits;
• number of turns per inch of length;
• group;
• accuracy class.

If you have a question, how to determine the type and size of thread Connecting fittings for pipes and hoses

connections use the table below.

Please note the following:

• connections with inch threads are highlighted in color
• next to the inch step size in tpi the step size in mm is indicated
• connections with external tapered threads usually do not have a threaded groove
• BSPT and NPT conical fittings are very similar, but BSPT has a mark on the hexagon

An important note - situations are quite possible when the inch and metric pitches are very close in size (this is possible on JIC connections).

Read also: Scraper conveyor operating principle

In this case, it is possible to confuse the inch thread. American cylindrical inch thread UNF (Unified Thread Standard)

UNC UNF and metric threads.

Threaded fasteners are one of the most popular for attaching parts, assembling products, equipment, and structures. There is no industry where it is not used. There are many thread characteristics: pitch, tolerance range, number of starts, nominal diameter, profile type and others. One of these is units of measurement, inches or millimeters.

There is often a situation when it is necessary to replace a bolt, pin or screw, but the fastener purchased for maximum similarity “by eye” is not screwed into the mounting hole. One of the reasons is an attempt to screw a fastener with an external inch thread into a hole with a metric thread. Or vice versa. This situation often arises when replacing fasteners on products or equipment manufactured in the UK, USA, Japan, or Australia. There, inch threads have priority.

How to distinguish an inch thread from a metric thread? There are two main ways - by measuring the pitch and diameter or using a special tool.

Measurement

Fastener thread markings are done differently in metric and inch systems. In metric, this is an indication of the thread pitch (the distance between adjacent threads) in millimeters, while in inch it is the number of threads per inch.

Determining the type and size of fastener thread comes down to the following operations. Use a caliper to measure the diameter. Then, using an inch ruler or caliper, measure the number of threads in one inch and the thread pitch. You can also use a regular ruler with measured 2.54 mm (1 inch = 2.54 mm). The metric thread pitch on small fasteners can be found by measuring the distance between 10 turns and dividing the resulting value by 10. The resulting values ​​should be compared with the table below. The maximum match in diameter, number of turns, pitch indicates the size and type of thread. It should be noted that there are many different types of inch threads. The table shows the most common ones in the diameter range from 8 mm to 64 mm.

You can also use a thread gauge to measure threads. This is its direct purpose. A thread gauge is a set of plates with protruding teeth for a specific thread, united on a single axis. The thread size is engraved or permanently inked on the plate itself. Checking the thread is done by applying plates that are closest in size to the thread. If there is a complete match, without gaps, the thread can be considered defined, and its size can be viewed on the thread gauge plate. Thread gauges are produced separately for metric, inch threads or both types.

Nuances of measurement

There are a few guidelines to keep in mind when using a caliper. An example is the information below:

1. If there is a plate between the head and the end part of the product, then in this case it is recommended to use the main measuring scale and depth gauge. With such a process, it is possible to obtain indicators of the thickness of the washer, the height of the head, and the thickness of the intermediate element. Such data allows you to calculate the main parameters of a threaded connection.
2. The accuracy of the results obtained can be significantly increased by cleaning the surface from various contaminants. To do this, you can use an abrasive material or special liquids to remove corrosion.

You can carry out the procedure in question yourself. As a rule, there are no problems with this.

In conclusion, we note that manufacturers indicate the pitch and many other important indicators. As a rule, they are applied to the head or other element.

The process of measuring turns

When considering how to determine the thread pitch, the features of the chosen method should be taken into account. When using a ruler it is enough:

1. Measure the length of the rod on which the profile was applied. It is worth considering that by measuring the entire length of the rod, and not just part, you can determine a more accurate result.
2. Count the number of turns.
3. Take depth measurements to determine the main parameters of the threaded connection.

In this way, only the average can be determined. If errors were made during the cutting process, the distance between them may differ slightly.

An example of measurements looks like this:

1. 20 turns are counted.
2. We measure the length of the rod, for example, the indicator was 127 mm.
3. We divide 20 turns by the length of the rod, the result is 6.35 mm. It corresponds to the pitch of the threads in millimeters.

To convert to inches, simply divide the calculated value in millimeters by 25.4. The result will be 0.25 or ¼ inch. If you measure yourself, there may be an error, so the result is rounded to an approximate standard value.

You can also find special templates on sale that can be used to check the features of the thread. This procedure is quite simple to perform:

1. The most suitable template is selected. On sale you can find simply a huge number of special templates, which are represented by a plate with a certain profile. Such an element is not expensive; you can purchase it in various specialized stores.
2. It is applied to the surface to monitor basic indicators. The template must fit without obstacles, and there should be no free space between the plate and the working surface.

If the template easily fits into the grooves, then the basic parameters of the surface can be determined.

Measuring thread pitch with a ruler and thread gauge

In addition, you can take measurements using a caliper. This tool has become widespread. The step-by-step actions are as follows:

1. The depth gauge determines the height of the rod.
2. The next step is to count the number of turns. This is quite difficult to do; you can use a marker to indicate the profile threads that have already been counted.
3. The information obtained allows you to calculate the tangent of the angle of inclination.

It is possible to determine the indicator in question by direct measurement between adjacent vertices. It is recommended to clean the surface. Otherwise, it is almost impossible to get an accurate result.

Rectangular thread

Table 3 presents data on rectangular threads.

Rectangular threads are most often made with a square tooth profile. But some manufacturers use rectangular profiles with an extended flange of the horizontal part for reinforcement

Table 3: Thread dimensions and helix pitch

Measurement methods

There are quite a large number of different ways to determine the thread pitch. All of them are characterized by their own specific features that need to be taken into account. Common methods include:

1. Using a regular ruler.
2. The use of a special tool that can be used to determine the value in question. A thread pitch meter can be purchased at a specialty store.
3. A caliper is a precision instrument. It is used quite often due to its high accuracy and versatility in use.

How to measure a thread

Article reading time: 10 minutes

Any threaded connection is formed by two elements, one of which has an internal thread and the second an external thread, for example, a bolt and nut, a screw and a mounting hole in the parts being connected, etc. To obtain a tight and high-quality connection, the geometric parameters of internal and external threads must match exactly.

These main parameters include:

• internal and external diameter;
• depth;
• thread pitch.

Therefore, when selecting fasteners for installation work, the question often arises of how to measure the thread. Measuring the diameter and depth of a cut is usually not difficult. A more difficult task will be to measure the thread pitch, and incorrect selection of parts according to this parameter will either not allow them to be tightened at all, or will significantly deteriorate the quality of the connection, making it virtually unusable.