SAE J532_201303 Standard includes complete general and dimensional specifications for those types of SAE filler and drain plugs having straight threads which are commonly used with gaskets or seals in automotive and related industrial applications.
References of SAE J532 standard as follows:
SAE J548/1 Spark Plugs
SAE J548/2 Spark Plug Installation Sockets
SAE J846 Coding Systems for Identification of Fluid Conductors and Connectors
ASTM B 1 1 7 Method of Salt Spray (Fog) Testing
Unified standard Class 2A external and Class 2B internal threads shall apply to inch sizes of plain finish (unplated) plugs and holes into which they assemble. For externally threaded parts with additive finish, the maximum diameters of Class 2A may be exceeded by the amount of the allowance, that is, the basic diameters (Class 2A maximum diameter plus the allowance) shall apply after plating.
Material and Manufacture
Plugs may be made from low carbon steel, cast iron, malleable iron, brass, bronze, or aluminum alloy as specified by purchaser, by casting, milling from the bar, or by upsetting from a grade of material free of defects which can adversely affect their serviceability.