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1、英制、公制对照表英寸制统一螺纹，在英寸制国家广泛采用，该类螺纹分三个系列：粗牙系列UNC，细牙系列UNF，特细牙系列UNFF，外加一个定螺距系列UN。标注方法：螺纹直径每英寸牙数 系列代号精度等级示例：粗牙系列 3/816 UNC2A 细牙系列 3/824 UNF2A特细牙系列 3/832 UNFF2A 定螺距系列 3/820 UN2A第一位数字3/8表示螺纹外径，单位为英寸，转换为米制单位mm要乘以25.4，即3/825.4=9.525mm；第二、三位数字16、24、32、20为每英寸牙数(在25.4mm长度上的牙数)；第三位以后的文字代号UNC、UNF、UNFF、UN为系列代号，最后两位2
2、A为精度等级。在统一螺纹标准中规定，一个公称尺寸可有不同的螺距，如1/2就有13牙、16牙、20牙、32牙之分，标准规定13牙为粗牙，20牙为细牙，28牙为超细牙；16牙和32牙都称为恒定螺距，与粗牙、细牙没什么不同。 英制螺纹外径公制对照表英制公制英制公制英制公制4#291-5/8412754-5/8117.4755#321-3/444454-3/4120.656#351-7/8476254-7/8123.8257#39250851278#422-1/8539755-1/4133.3510#482-1/457155-3/8136.52512#552-3/8603255-1/2139.714#
3、/1/46352-1/26355-5/8142.8751/831752-5/8666755-3/4146.051/46352-3/469855-7/8149.2255/1679362-7/8730256152.43/8952537626-1/4158.757/16111133-1/8793756-3/8161.9251/21273-1/482556-1/2168.2759/16142883-3/8857256-5/8171.455/8158753-1/28896-3/4174.6253/419053-5/8920256-7/8177.87/8222253-3/495.257184.151254
4、3-7/898.1257-1/4187.3251-1/8285754101.67-3/8190.51-1/431754-1/4107.957-1/2193.6751-3/8349254-3/8111.1257-5/8196.851-1/23814-1/2114.37-3/4200.025英美联合公制规格底孔规格底孔 1-64UNC1.55M1.0*0.250.752-56UNC1.8M1.1*0.250.853-48UNC2.1M1.2*0.250.954-40UNC2.3M1.4*0.31.15-40UNC2.6M1.6*0.351.256-32UNC2.8M1.7*0.351.358-32
5、UNC3.4M1.8*0.351.4510-32UNC4.1M2.0*0.41.610-24UNC3.9M2.2*0.451.7512-24UNC4.5M2.3*0.41.914-20UNC5.1M2.5*0.452.1516-18unc6.6M2.6*0.452.238-16UNC8M3.0*0.52.5716-14UNC9.4M3.0*0.62.412-13UNC10.8M3.5*0.62.9916-12UNC12.2M4.0*0.73.358-11UNC13.6M4.0*0.753.2534-10UNC16.5M4.5*0.73.878-9UNC19.5M5*0.84.21-8UNC22
6、.2M5*0.94.1118-7UNC25M6*1.05114-7UNC28.2M7*1.06138-6UNC30.8M8*1.256.8112-6UNC34M9*1.257.8134-5UNC39.5M10*1.58.52-412UNC45.2M11*1.59.5英美联合螺纹螺距根据每一英寸长度上拥有的牙数来计算外径根据螺纹牌号的第一个代号来计算（4#，5#，6#，7#，8#，10#，12#为特殊外径详见表1）例：1/4-20 UNC1/4*25.4=6.35（螺纹外径）25.4/20=1.27 （螺距）M12*1.7510.3M14*2.012M16*2.014M18*2.515M20*2
7、.517M22*2.519M24*3.021M27*3.024M30*3.526.5 螺纹电极外径，螺距参照表英美联合公制规格外径规格外径 1-64UNC1.45M1.0*0.250.652-56UNC1.7M1.1*0.250.753-48UNC2.0M1.2*0.250.854-40UNC2.2M1.4*0.31.05-40UNC2.5M1.6*0.351.156-32UNC2.7M1.7*0.351.258-32UNC3.3M1.8*0.351.3510-32UNC4.0M2.0*0.41.510-24UNC3.8M2.2*0.451.6512-24UNC4.4M2.3*0.41.814
8、-20UNC5.0M2.5*0.452.0516-18unc6.5M2.6*0.452.138-16UNC7.9M3.0*0.52.4716-14UNC9.3M3.0*0.62.312-13UNC10.7M3.5*0.62.8916-12UNC12.1M4.0*0.73.358-11UNC13.5M4.0*0.753.1534-10UNC16.4M4.5*0.73.778-9UNC19.4M5*0.84.11-8UNC22.1M5*0.94.0118-7UNC24.9M6*1.04.9114-7UNC28.1M7*1.05.9138-6UNC30.7M8*1.256.7112-6UNC33.9M9*1.257.7134-5UNC39.4M10*1.58.42-412UNC45.1M11*1.59.4英美联合螺纹螺距根据每一英寸长度上拥有的牙数来计算例：1/4-20 UNC1/4*25.4=6.35（螺纹外径）25.4/20=1.27 （螺距）阴影部为英制和公制粗牙常用螺纹M12*1.7510.2M14*2.011.9M16*2.013.9M18*2.514.9M20*2.516.9M22*2.518.9M24*3.020.9M27*3.023.9M30*3.526.5
