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 2.979 3.115 3.160 3.182 3.285 3.307 3.229 3.365 3.410 3.432 3.535 3.557 3.479 3.615 3.660 3.682 3.785 3.807 3.729 3.865 3.910 3.932 3.979 4.115 4.160 4.182 4.229
Max b 3.017 3.140 3.178 3.196 3.303 3.321 3.267 3.390 3.428 3.446 3.553 3.571 3.517 3.640 3.678 3.696 3.803 3.821 3.767 3.890 3.928 3.946 4.017 4.140 4.178 4.196 4.267
Min a
Max b
Max 2.998 3.128 3.169 3.189 3.294 3.314 3.248 3.378 3.419 3.439 3.544 3.564 3.498 3.628 3.669 3.689 3.794 3.814 3.748 3.878 3.919 3.939 3.998 4.128 4.169 4.189 4.248
Min 2.989 3.121 3.165 3.186 3.290 3.311 3.239 3.371 3.415 3.436 3.544 3.561 3.489 3.615 3.665 3.686 3.790 3.811 3.739 3.871 3.915 3.936 3.989 4.121 4.165 4.186 4.239
Max 3.008 3.134 3.174 3.193 3.299 3.318 3.258 2.384 3.424 3.443 3.549 3.568 3.508 3.634 3.674 3.693 3.799 3.818 3.758 3.884 3.924 3.943 4.008 4.134 4.174 4.193 4.258
Min 2.998 3.128 3.169 3.189 3.294 3.314 3.248 3.378 3.419 3.439 3.544 3.567 3.498 3.628 3.669 3.689 3.794 3.814 3.748 3.878 3.919 3.939 3.998 4.128 4.169 4.189 4.248
Min 3.008 3.134 3.174 3.193 3.299 3.317 3.258 3.384 3.424 3.443 3.549 3.568 3.508 3.634 3.674 3.693 3.799 3.818 3.758 3.884 3.924 3.943 4.008 4.134 4.174 4.193 4.258
Max 3.027 3.146 3.183 3.200 3.299 3.325 3.277 3.396 3.433 3.450 3.553 3.575 3.527 3.646 3.683 3.700 3.808 3.825 3.777 3.896 3.933 3.950 4.027 4.146 4.183 4.200 4.277
Max
Min
Max
Min
Min
Max
2.9790 2.9944 2.9869 3.0019 2.9944 3.0094 3.0019 3.0169 3.1150 3.1222 3.1184 3.1259 3.1222 3.1297 3.1260 3.1335 3.1600 3.1648 3.1623 3.1673 3.1648 3.1698 3.1673 3.1723 3.1820 3.1866 3.1844 3.1887 3.1865 3.1908 3.1886 3.1929 3.2850 3.2898 3.2873 3.2923 3.2898 3.2948 3.2923 3.2973 3.3070 3.3116 3.3094 3.3137 3.3115 3.3158 3.3136 3.3179 3.2290 3.2444 3.2369 3.2519 3.2444 3.2594 3.2519 3.2669 3.3650 3.3722 3.3684 3.3759 3.3722 3.3797 3.3760 3.3835 3.4100 3.4148 3.4123 3.4173 3.4148 3.4198 3.4173 3.4223 3.4320 3.4366 3.4344 3.4387 3.4365 3.4408 3.4386 3.4429 3.5350 3.5398 3.5373 3.5423 3.5398 3.5448 3.5423 3.5473 3.5570 3.5616 3.5594 3.5637 3.5615 3.5658 3.5636 3.5679 3.4790 3.4944 3.4869 3.5019 3.4944 3.5094 3.5019 3.5169 3.6150 3.6222 3.6184 3.6259 3.6222 3.6297 3.6260 3.6335 3.6600 3.6648 3.6623 3.6673 3.6648 3.6698 3.6673 3.6723 3.6820 3.6866 3.6844 3.6887 3.6865 3.6908 3.6886 3.6929 3.7850 3.7898 3.7873 3.7923 3.7898 3.7948 3.7923 3.7973 3.8070 3.8116 3.8094 3.8137 3.8115 3.8158 3.8136 3.8179 3.7290 3.7444 3.7369 3.7519 3.7444 3.7594 3.7519 3.7669 3.8650 3.8722 3.8684 3.8759 3.8722 3.8797 3.8760 3.8835 3.9100 3.9148 3.9123 3.9173 3.9148 3.9198 3.9173 3.9223 3.9320 3.9366 3.9344 3.9387 3.9365 3.9408 3.9386 3.9429 3.9790 3.9944 3.9869 4.0019 3.9944 4.0094 4.0019 4.0169 4.1150 4.1222 4.1184 4.1259 4.1222 4.1297 4.1260 4.1335 4.1600 4.1648 4.1623 4.1673 4.1648 4.1698 4.1673 4.1723 4.1820 4.1866 4.1844 4.1887 4.1865 4.1908 4.1886 4.1929 4.2290 4.2444 4.2369 4.2519 4.2444 4.2594 4.2519 4.2669
3 1 ∕ 4 -4 3 1 ∕ 4 -8 3 1 ∕ 4 -12 3 1 ∕ 4 -16 3 3 ∕ 8 -12 3 3 ∕ 8 -16 3 1 ∕ 2 -4 3 1 ∕ 2 -8 3 1 ∕ 2 -12 3 1 ∕ 2 -16 3 5 ∕ 8 -12 3 5 ∕ 8 -16 3 3 ∕ 4 -4 3 3 ∕ 4 -8 3 3 ∕ 4 -12 3 ∕ 4 -16 3 7 ∕ 8 -12 3 7 ∕ 8 -16
4-4 4-8 4-12 4-16
4 1 ∕ 4 -4 4 1 ∕ 4 -8 4 1 ∕ 4 -12 4 1 ∕ 4 -16 4 1 ∕ 2 -4
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