Understanding Metric FastenersPhoto From pexels

Originally Posted On: https://www.mudgefasteners.com/news/2020/2/26/understanding-metric-fasteners


The size of a metric fastener is specified by diameter, pitch and length, in millimeters (mm). For nuts, size will appear as diameter and pitch. When pitch isn’t specified, the fastener is considered coarse thread by default. Consider this example:

M10-1.0 x 20

Let’s take a closer look at what that description means:

  • M = Metric designation

  • 10 = Nominal diameter (mm)

  • 1.0 = Thread pitch (distance from thread to thread), in millimeters

  • 20 = Length (mm)

This example illustrates how a coarse threaded screw may appear:

An M10 x 25 description would mean the diameter is 10 mm, and since there is no thread pitch listed, coarse thread is assumed, with a 25 mm length. An M10 nut would be the matching coarse threaded nut.

If you’re used to working with inch fasteners, pitch can be a confusing, but thread pitch just means the distance between adjacent threads. In the example above, a thread pitch of 1.0 means that from one thread to the next thread, the distance is 1.0 millimeter. Inch fasteners are classified by threads per inch, meaning a 1/4-20 bolt has 20 threads per inch, whereas a 3/8-16 bolt has 16 threads per inch. To determine the threads per inch of a metric fastener, convert thread pitch from millimeters to inches (multiply by 0.03937), then divide 1 by that number.

At Mudge Fasteners, we’re here to help. If you have questions about any of the dimensions of metric fasteners, or need help with conversions, just contact us. We have also created some handy brochures to assist you, including our metric line card and metric conversion chart with selection guide.