SAE J1231 Dimensions and Tolerances including hexagons, thread, nominal sizes, drilled holes, passages, contour, straight threads etc. Details as follows:
Hexagons dimensions tolerances: The minimum across corners dimensions of external hexagons shall be 1.092 times the nominal width across flats, but shall not result in a side flat width of less than 0.43 times the nominal width across flats.
Tolerance on all dimensions not otherwise limited shall be ±0.25 mm. Angular tolerance on axis of ends on elbows shall be ±2.50 degrees for sizes up to and including 9.52 mm and ±1.50 degrees for sizes larger than 9.52 mm.
Tolerance on hole diameters: designated as a drill in the dimensional tables (Tables 3, 4, and 5) shall conform to Table 1:
Passages tolerance: in straight fittings are machined from opposite ends, the offset at the meeting point shall not exceed 0.40 mm.
Contour tolerances shall be optional with manufacturer provided the tabulated dimensions are maintained and serviceability of the fittings is not impaired.
Straight Threads Unified Standard Class 2A external and Class 2B internal threads shall apply to plain finish (unplaced) fittings having straight threads designated A1 in Figure 3 and Table 5.
Taper pipe threads designated A in Figure 2 and Table 4 shall conform to the Dryseal American Standard Taper Pipe Thread (NPTF). Specifications are given in detail in SAE J476. At purchaser's option, the pipe thread may be shortened in conformity with the SAE Short Dryseal Taper Pipe Thread (PTF-SAE Short).