How To Measure Thread Size Of A Bolt. Due to the excellent performance and low price, the u bolt is a superb steel fastener throughout the industry. For example, if your bolt has a diameter of 4mm then it is called an 'm4 bolt' if your bolt is imperial then it will be measured in inches.
Grab a ruler and lay it along the bolt or screw. Iso 4014, iso 4017, iso 4032, iso 4762 For the size m6 × 1 mm, the pitch is coarse;
For example a m5x10 bolt has a 5mm shaft diameter and is 10mm long from the bottom of the head to the end of the fastener.
The necessary tapping hole size can be easily calculated by deducting the thread pitch from the metric bolt diameter. Do not measure the head of the bolt, measure the threaded part, outside of the threads. For example, if your bolt has a diameter of 4mm then it is called an 'm4 bolt' if your bolt is imperial then it will be measured in inches. The bolt depot has some excellent charts that you can print off for both imperial and metric fasteners, as well as nuts and washers.