Common screw specifications and markings

A: Metric screw
B: US screw
C: Inch screw
A: Metric Machine Screw: Metric
Ex: M3 x 6 – P P B : M3 machine screw, 6mm long, cross, flat head, black plated.
Finish Code: Appearance Treatment Specifications
Head Code: head shape
Thread Code
Screw model Drive Code: head groove, characteristic model
Length Code: screw length (mm)
A-1: Thread Code: Screw Type
For metric screws, the screw type is directly marked with the outer diameter of the screw.
For example, M3 means the outer diameter of the screw is 3.00mm.; M4 means the outer diameter of the screw is 4.00mm.
Metric Thread Size x Pitch:
Note: Metric screws are at the back of the screw model, sometimes the screw pitch is indicated.
Such as M3x0.5 , M4x0.70 , M5x0.8 , M6x1.
But because of the standard specification, it is usually not mentioned.
A-2: Length Code: Screw Length:
Metric screws, directly indicate the length of the screw, the unit is mm.
The total length of the screw is indicated, only the length below the head is calculated, excluding the height of the head.
With the exception of flat head screws, the total length of the screw is marked with the head height.
A-3: Drive Code/ Head groove, features.