圈上大峰 Identification Codes2 .Naming Convention for -20 UNC -2A English Units Thread class symbol Thread form.scries,and tolerance svmbo Number of threads per inch Nominal outside diamerer,nominal size .Naming Convention for ￥0×12-h6h Metric Units Crest diameer tolerance position Tolrance grade for crest diameter .Right hand assumed Tokrance grade for pitch diamee Pitch in mm.thread unless designation is Outside diameer,nominal sie,mm followed by-LH.(左旋) 圈上我大峰 Tolerances and Allowances2 Allowances(配合余量) >Specify the clearance()provided for nuts and screws to accommodate coatings and/or foreign material after mating Tolerances(公差) >Specify limits on acceptable manufacturing errors in producing screws and nuts to comply with standard profiles and dimensions. .Applied to screws and nuts major and minor diameters. 3837 Identification Codes2 •Naming Convention for English Units •Naming Convention for Metric Units •Right hand assumed unless designation is followed by -LH.（左旋） 38 •Allowances（配合余量） Specify the clearance(间隙) provided for nuts and screws to accommodate coatings and/or foreign material after mating •Tolerances（公差） Specify limits on acceptable manufacturing errors in producing screws and nuts to comply with standard profiles and dimensions. •Applied to screws and nuts major and minor diameters. Tolerances and Allowances2