Metric Fasteners

Machine Screws

ISO metric machine screws are limited to four different head shapes: countersunk, raised countersunk, panhead, and chiselhead. All head dimensions are directly related to the basic screw diameter as follows:

Size Min.Length mm    Size Min.Length mm
M1.6 15 M6 28
M2 16 M8 34
M2.5 18   M10 40
M3 19   M12 46
M4 22   M16 58
M5 25   M20 70

Socket Screws

ISO metric hexagon socket screws are limited to two different head shapes: cap screw, and countersunk socket screw.All head dimensions are directly related to the basic screw diameter as follows:

Size Min. Length (mm)   Size Min. Length (mm)
M3 3   M8 20
M4 10   M10 25
M5 12   M12 30
M6 16 M14  35

Nuts and Washers

The nut and washer dimensions are related to the basic screw diameter as follows: 

NONSTRUCTURAL   s=1.6 D  e=1.8 D  m=0.8 D
(Plain) m=0.5 D (Thin)
STRUCTURAL   s=1.8 D  e=2 D  m=0.9 D  

Bolts

Bolt head dimensions are related to their diameter as follows:

NONSTRUCTURAL   s=1.6 D  e=1.8 D  k=0.7 D  
STRUCTURAL   s=1.8 D  e=2 D  m=0.7 D