Metric external thread dimensions are given in the external thread chart below according to ASME B1.13M standard. Thread pitch diameter, major diameter and minor diameter
for M profile external threads are given. All dimensions are in millimeters.
Threads produced to ASME B1.13M standard are fully interchangeable
with threads that are based on ISO 68-1 basic profile and
ISO 965-1 tolerance practices.
External Thread Tolerance Classes:
- for normal tolerance — tolerance class 6g
- for tighter tolerance — tolerance class 4g6g
- for a no-allowance fit at maximum material, such
as for a plated 6g — tolerance class 6h
Size limits for standard
external thread tolerance classes 6g and 4g6g apply prior
to coating. The external thread
allowance may thus be used to accommodate the coating thickness on coated parts.
The designation of a screw thread gives
the thread symbol, the nominal size, the pitch, and the
thread tolerance class (Ex: M6 x 1 - 4g6g). In tolerance class designation, the pitch diameter tolerance is followed by major diameter tolerance. If the two class designations for the pitch diameter and
major diameter are same, it is not necessary to repeat the symbols. (Ex: M6 x 1 - 6g)
General Note: All dimensions are in millimeters.
Note-1: Maximum rounded form minor diameter is calculated with following formula. The rest of the dimensions are tabulated values from the ASME standard.
Maximum rounded form minor diameter = d3max = d2max - (0.5H + 2rmin (1 − cos
− arccos(1 −
4rmin)))). Here, rmin is minimum root radius, Td2 is pitch diameter tolerance
and H is height of sharp V-thread.