5/16-18unc-2B;大径min:0.3125中径0.2764~0.2817小径0.252~0.2653/8-16UNC-2B大径min:0.3750中径03344~0.3401小径0.307~0.3211/2-20UNF-2B大径min:0.5000中径0.4675~0.4731小径0.446~0.457备注:将上述尺寸X25.4即可换算为公制毫米。
大经9.525中经8.73125小径7.9375