How To Measure Thread Size Of A Bolt. The necessary tapping hole size can be easily calculated by deducting the thread pitch from the metric bolt diameter. The important thing here is that you need to print them out at actual size.
How bolt sizes are expressed. The important thing here is that you need to print them out at actual size. For the size m6 × 1 mm, the pitch is coarse;
Measure the outside diameter of the bolt threads using a vernier caliper.
You will need both the thread diameter and the thread pitch to determine the thread size. The thread diameter is what is referred to as the bolt's size on the product package. Metric thread sizes are specified by diameter and pitch, which is the space between threads. Do not measure the head of the bolt, measure the threaded part, outside of the threads.