Labcradle Pack of 100 Food Grade Stainless Steel Metric Screw M4 x 20 Bag of Screws

Metric Screws for European and Asian Equipment, Scientific Equipment 4mm diameter and 20mm length

The ISO metric screw thread

The "M" stands for the nominal outer diameter of the screw thread, in millimetres.

It also indicates the diameter of the hole that a male thread can go into.

M4 screw has a nominal diameter of 3.7mm and will fit in a hole drilled to 4 mm diameter