The following table chart defines standard metric external thread size M1.6 to M18 per. ANSI/ASME B1.13M-1995. These thread sizes and classes represent bolts and screws, as well, as other standard external threads. Do not use these values for standard metric internal thread design. All units in mm.
H = P ( 31/2 / 2 ) = 0.866025 P
0.125H = 0.108253P
Engineering Slide Chart ANSI Screw & Hardware Selector