Table 3. Recommended Hole Size Limits Before Tapping Unified Threads Table 3. (Continued) Recommended Hole Size Limits Before Tapping Unified Threads
Classes 1B and 2B
Class 3B
Length of Engagement ( D = Nominal Size of Thread)
Thread Size
Above 2 ∕ 3 D to 1 1 ∕ 2 D
Above 1 1 ∕ 2 D to 3 D
Above 2 ∕ 3 D to 1 1 ∕ 2 D
Above 1 1 ∕ 2 D to 3 D
Above 1 ∕ 3 D to 2 ∕ 3 D
Above 1 ∕ 3 D to 2 ∕ 3 D
To and Including 1 ∕ 3 D
To and Including 1 ∕ 3 D
Recommended Hole Size Limits
Min a 0.745 0.758 0.755 0.785 0.798 0.807 0.821 0.836 0.847 0.870 0.883 0.865 0.910 0.923 0.932 0.946 0.961 0.972 0.995 1.002 0.970 0.990 1.035 1.057 1.065 1.071 1.086 1.097
Max b 0.759 0.770 0.778 0.803 0.814 0.821 0.832 0.845 0.865 0.884 0.895 0.890 0.928 0.938 0.946 0.957 0.970 0.990 1.009 1.015 0.998 1.015 1.053 1.071 1.078 1.082 1.095 1.115
Min a
Max b
Max 0.752 0.764 0.767 0.794 0.806 0.814 0.827 0.840 0.856 0.877 0.889 0.878 0.919 0.931 0.939 0.952 0.966 0.981 1.002 1.009 0.984 1.003 1.044 1.064 1.072 1.077 1.091 1.106
Min 0.749 0.761 0.761 0.790 0.802 0.811 0.824 0.838 0.852 0.874 0.886 0.871 0.915 0.927 0.936 0.949 0.963 0.977 0.999 1.005 0.977 0.996 1.040 1.061 1.068 1.074 1.088 1.102
Max 0.756 0.766 0.773 0.799 0.810 0.818 0.829 0.843 0.861 0.881 0.891 0.884 0.924 0.934 0.943 0.954 0.968 0.986 1.055 1.012 0.991 1.009 1.049 1.068 1.075 1.079 1.093 1.111
Min 0.752 0.764 0.767 0.794 0.806 0.814 0.827 0.840 0.856 0.877 0.889 0.878 0.919 0.931 0.939 0.952 0.966 0.981 1.002 1.009 0.984 1.003 1.044 1.064 1.072 1.077 1.091 1.106
Min 0.756 0.766 0.773 0.799 0.810 0.818 0.829 0.843 0.861 0.881 0.891 0.884 0.924 0.934 0.943 0.954 0.968 0.986 1.055 1.012 0.991 1.009 1.049 1.068 1.075 1.079 1.093 1.111
Max 0.763 0.772 0.785 0.808 0.818 0.825 0.835 0.847 0.870 0.888 0.897 0.896 0.933 0.942 0.950 0.960 0.972 0.995 1.013 1.018 1.005 1.021 1.058 1.075 1.081 1.085 1.097 1.120
Max
Min
Max
Min
Min
Max
0.7450 0.7491 0.7469 0.7512 0.7490 0.7533 0.7511 0.7554 0.7580 0.7623 0.7602 0.7642 0.7622 0.7662 0.7641 0.7681 0.7550 0.7614 0.7580 0.7647 0.7614 0.7681 0.7647 0.7714 0.7850 0.7900 0.7874 0.7926 0.7900 0.7952 0.7926 0.7978 0.7980 0.8022 0.8000 0.8045 0.8023 0.8068 0.8045 0.8090 0.8070 0.8116 0.8094 0.8137 0.8115 0.8158 0.8136 0.8179 0.8210 0.8248 0.8227 0.8267 0.8247 0.8287 0.8266 0.8306 0.8360 0.8395 0.8370 0.8410 0.8386 0.8426 0.8402 0.8442 0.8470 0.8524 0.8499 0.8550 0.8524 0.8575 0.8550 0.8601 0.8700 0.8741 0.8719 0.8762 0.8740 0.8783 0.8761 0.8804 0.8830 0.8873 0.8852 0.8892 0.8872 0.8912 0.8891 0.8931 0.8650 0.8722 0.8684 0.8759 0.8722 0.8797 0.8760 0.8835 0.9100 0.9148 0.9123 0.9173 0.9148 0.9198 0.9173 0.9223 0.9230 0.9271 0.9249 0.9293 0.9271 0.9315 0.9293 0.9337 0.9320 0.9366 0.9344 0.9387 0.9365 0.9408 0.9386 0.9429 0.9460 0.9498 0.9477 0.9517 0.9497 0.9537 0.9516 0.9556 0.9610 0.9645 0.9620 0.9660 0.9636 0.9676 0.9652 0.9692 0.9720 0.9773 0.9748 0.9798 0.9773 0.9823 0.9798 0.9848 0.9950 0.9991 0.9969 1.0012 0.9990 1.0033 1.0011 1.0054 1.0020 1.0065 1.0044 1.0085 1.0064 1.0105 1.0085 1.0126 0.9700 0.9790 0.9747 0.9833 0.9789 0.9875 0.9832 0.9918 0.9900 0.9972 0.9934 1.0009 0.9972 1.0047 1.0010 1.0085 1.0350 1.0398 1.0373 1.0423 1.0398 1.0448 1.0423 1.0473 1.0570 1.0616 1.0594 1.0637 1.0615 1.0658 1.0636 1.0679 1.0650 1.0690 1.0669 1.0710 1.0689 1.0730 1.0710 1.0751 1.0710 1.0748 1.0727 1.0767 1.0747 1.0787 1.0766 1.0806 1.0860 1.0895 1.0870 1.0910 1.0886 1.0926 1.0902 1.0942 1.0970 1.1023 1.0998 1.1048 1.1023 1.1073 1.1048 1.1098
13 ∕ 16 -16 13 ∕ 16 -20
7 ∕ 8 -9 7 ∕ 8 -12 7 ∕ 8 -14 7 ∕ 8 -16 7 ∕ 8 -20 7 ∕ 8 -28
15 ∕ 16 -12 15 ∕ 16 -16 15 ∕ 16 -20
1-8 1-12 1-14 1-16 1-20 1-28
1 1 ∕ 16 -12 1 1 ∕ 16 -16 1 1 ∕ 16 -18 1 1 ∕ 8 -7 1 1 ∕ 8 -8 1 1 ∕ 8 -12 1 1 ∕ 8 -16 1 1 ∕ 8 -18 1 1 ∕ 8 -20 1 1 ∕ 8 -28 1 3 ∕ 16 -12
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