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 1.490 1.535 1.557 1.565 1.620 1.627 1.534 1.615 1.660 1.682 1.696 1.745 1.740 1.785 1.807 1.870 1.759 1.865 1.910 1.932 1.946 1.995 1.990 2.035 2.057 2.120 2.009
Max b 1.515 1.553 1.571 1.578 1.634 1.640 1.568 1.640 1.678 1.696 1.707 1.759 1.765 1.803 1.821 1.884 1.795 1.890 1.928 1.946 1.957 2.009 2.015 2.053 2.071 2.134 2.045
Min a
Max b
Max 1.498 1.544 1.564 1.572 1.627 1.634 1.551 1.628 1.669 1.689 1.702 1.752 1.752 1.794 1.814 1.877 1.777 1.878 1.919 1.939 1.952 2.002 2.003 2.044 2.064 2.127 2.027
Min 1.494 1.540 1.561 1.568 1.624 1.630 1.543 1.621 1.665 1.686 1.699 1.749 1.746 1.790 1.810 1.874 1.768 1.871 1.915 1.936 1.949 2.000 1.996 2.040 2.061 2.124 2.018
Max 1.509 1.549 1.568 1.575 1.631 1.637 1.560 1.634 1.674 1.693 1.704 1.756 1.759 1.799 1.818 1.881 1.786 1.884 1.924 1.943 1.954 2.006 2.009 2.049 2.068 2.131 2.036
Min 1.498 1.544 1.564 1.572 1.627 1.634 1.551 1.628 1.669 1.689 1.702 1.752 1.752 1.794 1.814 1.877 1.777 1.878 1.919 1.939 1.952 2.002 2.003 2.044 2.064 2.127 2.027
Min 1.509 1.549 1.568 1.575 1.631 1.637 1.560 1.634 1.674 1.693 1.704 1.756 1.759 1.799 1.818 1.881 1.786 1.884 1.924 1.943 1.954 2.006 2.009 2.049 2.068 2.131 2.036
Max 1.521 1.558 1.575 1.581 1.638 1.643 1.577 1.646 1.683 1.700 1.710 1.763 1.771 1.808 1.825 1.888 1.804 1.896 1.933 1.950 1.960 2.012 2.021 2.058 2.075 2.138 2.054
Max
Min
Max
Min
Min
Max
1.4900 1.4972 1.4934 1.5009 1.4972 1.5047 1.5010 1.5085 1.5350 1.5398 1.5373 1.5423 1.5398 1.5448 1.5423 1.5473 1.5570 1.5616 1.5594 1.5637 1.5615 1.5658 1.5636 1.5679 1.5650 1.5690 1.5669 1.5710 1.5689 1.5730 1.5710 1.5751 1.6200 1.6241 1.6219 1.6262 1.6240 1.6283 1.6261 1.6304 1.6270 1.6315 1.6294 1.6335 1.6314 1.6355 1.6335 1.6376 1.5340 1.5455 1.5395 1.5515 1.5455 1.5575 1.5515 1.5635 1.6150 1.6222 1.6184 1.6259 1.6222 1.6297 1.6260 1.6335 1.6600 1.6648 1.6623 1.6673 1.6648 1.6698 1.6673 1.6723 1.6820 1.6866 1.6844 1.6887 1.6865 1.6908 1.6886 1.6929 1.6960 1.6998 1.6977 1.7017 1.6997 1.7037 1.7016 1.7056 1.7450 1.7491 1.7469 1.7512 1.7490 1.7533 1.7511 1.7554 1.7400 1.7472 1.7434 1.7509 1.7472 1.7547 1.7510 1.7585 1.7850 1.7898 1.7873 1.7923 1.7898 1.7948 1.7923 1.7973 1.8070 1.8116 1.8094 1.8137 1.8115 1.8158 1.8136 1.1879 1.8700 1.8741 1.8719 1.8762 1.8740 1.8783 1.8761 1.8804 1.7590 1.7727 1.7661 1.7794 1.7728 1.7861 1.7794 1.7927 1.8650 1.8722 1.8684 1.8759 1.8722 1.8797 1.8760 1.8835 1.9100 1.9148 1.9123 1.9173 1.9148 1.9198 1.9173 1.9223 1.9320 1.9366 1.9344 1.9387 1.9365 1.9408 1.9386 1.9429 1.9460 1.9498 1.9477 1.9517 1.9497 1.9537 1.9516 1.9556 1.9950 1.9991 1.9969 2.0012 1.9990 2.0033 2.0011 2.0054 1.9900 1.9972 1.9934 2.0009 1.9972 2.0047 2.0010 2.0085 2.0350 2.0398 2.0373 2.0423 2.0398 2.0448 2.0423 2.0473 2.0570 2.0616 2.0594 2.0637 2.0615 2.0658 2.0636 2.0679 2.1200 2.1241 2.1219 2.1262 2.1240 2.1283 2.1261 2.1304 2.0090 2.0227 2.0161 2.0294 2.0228 2.0361 2.0294 2.0427
1 5 ∕ 8 -8 1 5 ∕ 8 -12 1 5 ∕ 8 -16 1 5 ∕ 8 -18 1 3 ∕ 4 -5 1 3 ∕ 4 -8 1 3 ∕ 4 -12 1 3 ∕ 4 -16 1 11 ∕ 16 -16 1 11 ∕ 16 -18 1 3 ∕ 4 -20 1 13 ∕ 16 -16
1 7 ∕ 8 -8 1 7 ∕ 8 -12 1 7 ∕ 8 -16
1 15 ∕ 16 -16
2-4 1 ∕ 2 2-8 2-12 2-16 2-20
2 1 ∕ 16 -16 2 1 ∕ 8 -8 2 1 ∕ 8 -12 2 1 ∕ 8 -16 2 3 ∕ 16 -16 2 1 ∕ 4 -4 1 ∕ 2
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