M10-thread: how is it?

One of the achievements that played an important role in accelerating the scientific and technological progress that distinguishes the last 500 years of human history is the invention of a threaded joint. Let's take a closer look at its features.

Rivets and wedges

In ancient times, the strength of prefabricated structures was given by such means of joining as wedges (in wooden products) and rivets (in metal products). The main drawback of such connections has been and remains the inability to reuse fasteners.

Wedges and rivets have a one-time use, and this requires unnecessary costs. The first threads also had a significant limitation, since they were not made on cutting machines, but by means of patterns, with which the thread was forged on a hot metal. On the interchangeability of parts that had an external and internal thread, made in this way, it was not.

Metric thread

In most countries of the world, a metric measurement system is adopted, based on the conventionality that one meter is a thousand millimeters. This system of measurement and the production of machines that were gaining momentum led to a wide distribution of metric threads and the simplicity of its designation. For example, the designation M10 (thread) - here the letter "M" indicates its diameter in the metric system of measurements.

However, these are not all the parameters that characterize a threaded connection. In this case, in the characteristic "thread M10", the diameter is indicated by the number 10, it indicates the outer diameter of the bolt . In addition to the thread diameter, there is still such an indicator as the thread pitch.

Depending on the strength of the connection, the thread pitch can be different. Thus, the standard thread M10 can have the following step values:

• 0.5 mm;
• 0,75 mm;
• 1 mm;
• 1.25 mm.

For the largest standard thread, the step in its designation may not be indicated, since it is taken as the main one. So, if we see the designation M10, and after that there are no additions, then by default this M10-thread has a step of 1.25 millimeters.

Internal metric thread

Naturally, in order for the threaded connection to be applied, two threads must be combined, cut at the appropriate places of the parts to be joined:

• External - on a bolt or hairpin;
• Internal - in the nut or body of the part.

In the part in which the M10 internal thread will be used, the hole must be drilled to take into account the length and pitch. This diameter is often easy to compute with elementary knowledge in mathematics and even not having tables with standard values at hand, since the metric standard for threading has a profile angle of 60 degrees.

The rules of an isosceles triangle and the Pythagorean theorem make it easy to determine that the thread height in steps of 1 millimeter is 0.866 millimeters. Thus, the hole in which the M10-thread will be created must be at least 8.268 mm:

10 - 0.866 - 0.866 = 0.8268

Since the thread is on both sides of the drilling axis, the thread height is taken from the outer diameter twice.

Why there is a different step

As already mentioned, depending on the required strength of the connection, a different thread pitch is used. The most common among those used in engineering and other fields is a major step. However, for a higher strength of the connection, a small thread pitch is also used.

It, in addition, is also used wherever greater precision is required. For example, in a measuring instrument of higher accuracy than a caliper, a metric thread with a small or very small thread pitch is used. In this case, the translational movement, the size of which needs to be measured, is divided into the length of the thread circumference, which makes it possible to measure not only tenths but also hundredths of a millimeter.

Naturally, a large thread pitch prevents accurate measurement. After M10-thread with a large step of 1.25 millimeters will have a measuring accuracy of two and a half times smaller than with a very small step of 0.5 millimeters.

It is worth noting that because of the more complicated (from the point of view of technology) obtaining threads with a very small pitch, it is practically not used in engineering. The main area of its application is a measuring instrument.

Although most of the threaded connections have a right-hand thread (to twist the bolt, it must be rotated clockwise), if necessary, the left thread can be used. For example, the bicycle pedal kit has a left and right mounting thread.