How to Measure Screws and Bolts Correctly
Correct measurement is the quickest way to avoid ordering the wrong replacement fastener. A useful identification includes nominal thread diameter, thread pitch, length, head style, drive style and the material or finish rather than only one visible dimension.
How to Read Metric Screw Sizes: M3, M4, M5 & M6 Explained
Labels such as M3×8, M4×12 and M6×20 tell you much more than a random stock code. The first number identifies the nominal metric thread diameter and the second number normally.