The following table chart are standard metric internal thread sizes M 0.25 - M 8 per. ANSI/ASME B1.13M-1995. These thread sizes and classes represent bolts and screws, as well, as other standard internal threads. Do not use these values for standard metric external thread design. All units in mm.
H = P ( 31/2 / 2 ) = 0.866025 P
0.125H = 0.108253P