公称尺寸和每英寸牙数 大径极限 中径极限 小径max 螺胚直径

美制螺纹标准对照表

美制外螺纹（2A）常用规格极限尺寸表（粗牙）

 公称尺寸和螺纹系列每英寸牙数代号 8‐32(0.164‐32) 10‐24(0.190‐24) 12‐24(0.216‐24) 1/4‐20(0.250‐20) 5/16‐18(0.3175‐18) 3/8‐16(0.375‐16) 7/16‐14(0.4375‐14) 1/2‐13(0.50‐13)9/16/2012(0.5625‐12) 5/8‐11(0.625‐11) 3/4‐10(0.750‐10) 7/8‐9(0.875‐9)1"‐8(1.000‐8)

大径极限最小0.15713.99030.18184.61770.20785.27810.24086.11630.30267.6860.36439.25320.425810.81530.487612.3850.549513.95730.611315.5270.735318.67660.859221.82370.98324.9682

最大0.16314.14270.1894.80060.2155.4610.24896.32210.31137.9070.37379.4920.436111.07690.498512.66190.560914.24690.623415.83440.748219.00430.873122.17670.99825.3492

中径极限最小0.13993.55350.15864.02840.18454.68630.21275.40260.27126.88850.32878.3490.3859.7790.443511.26490.501612.74060.558914.19610.677317.20340.794620.18280.9123.114

最大0.14283.62710.16194.11230.18794.77270.21645.49660.27526.99010.33318.46070.38979.89840.448511.39190.506812.87270.564414.33580.683217.35330.800920.34290.916823.2867

小径max0.12483.16990.13793.50270.16394.16310.18764.7650.24316.17470.2977.54380.34858.85190.404110.26410.458711.6510.511913.00230.625515.88770.736818.71470.844621.4528

螺胚直径最小3.584.074.725.456.948.49.8311.3412.814.2717.2820.2723.22

最大3.614.14.755.486.988.449.8711.3812.8414.3217.3320.3223.27

UNC

1.螺胚直径指滚丝前的尺寸，数值为依经验公式计算而得，在实践中需验证。2.标记示例：10‐24UNC‐2A(或0.190‐24UNC‐2A)、3/8‐16UNC‐2A(或0.375‐16UNC‐2A)（注：表中上行斜体数值单位为英寸，下行为毫米）