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 4.365 4.410 4.432 4.615 4.660 4.682 4.865 4.910 4.932 5.115 5.160 5.182 5.365 5.410 5.432 5.615 5.660 5.682 5.865 5.910 5.932
Max b 4.390 4.428 4.446 4.640 4.678 4.696 4.890 4.928 4.946 5.140 5.178 5.196 5.390 5.428 5.446 5.640 5.678 5.696 5.890 5.928 5.946
Min a
Max b
Max 4.378 4.419 4.439 4.628 4.669 4.689 4.878 4.919 4.939 5.128 5.169 5.189 5.378 5.419 5.439 5.628 5.669 5.689 5.878 5.919 5.939
Min 4.371 4.419 4.437 4.621 4.665 4.686 4.871 4.915 4.936 5.121 5.165 5.186 5.371 5.415 5.436 5.621 5.665 5.686 5.871 5.915 5.935
Max 4.384 4.424 4.444 4.646 4.674 4.693 4.884 4.924 4.943 5.134 5.174 5.193 5.384 5.424 5.442 5.634 5.674 5.693 5.896 5.924 5.943
Min 4.378 4.419 4.439 4.628 4.669 4.689 4.878 4.919 4.939 5.128 5.169 5.189 5.378 5.419 5.439 5.628 5.669 5.689 5.878 5.919 5.939
Min 4.384 4.424 4.444 4.646 4.674 4.693 4.884 4.924 4.943 5.134 5.174 5.193 5.384 5.424 5.442 5.634 5.674 5.693 5.896 5.924 5.943
Max 4.396 4.433 4.455 4.646 4.683 4.700 4.896 4.933 4.950 5.146 5.183 5.200 5.396 5.433 5.450 5.646 5.683 5.700 5.896 5.933 5.950
Max
Min
Max
Min
Min
Max
4.3650 4.3722 4.3684 4.3759 4.3722 4.3797 4.3760 4.3835 4.4100 4.4148 4.4123 4.4173 4.4148 4.4198 4.4173 4.4223 4.4320 4.4366 4.4344 4.4387 4.4365 4.4408 4.4386 4.4429 4.6150 4.6222 4.6184 4.6259 4.6222 4.6297 4.6260 4.6335 4.6600 4.6648 4.6623 4.6673 4.6648 4.6698 4.6673 4.6723 4.6820 4.6866 4.6844 4.6887 4.6865 4.6908 4.6886 4.6929 4.8650 4.8722 4.8684 4.8759 4.8722 4.8797 4.8760 4.8835 4.9100 4.9148 4.9123 4.9173 4.9148 4.9198 4.9173 4.9223 4.9320 4.9366 4.9344 4.9387 4.9365 4.9408 4.9386 4.9429 5.1150 5.1222 5.1184 5.1259 5.1222 5.1297 5.1260 5.1335 5.1600 5.1648 5.1623 5.1673 5.1648 5.1698 5.1673 5.1723 5.1820 5.1866 5.1844 5.1887 5.1865 5.1908 5.1886 5.1929 5.3650 5.3722 5.3684 5.3759 5.3722 5.3797 5.3760 5.3835 5.4100 5.4148 5.4123 5.4173 5.4148 5.4198 5.4173 5.4223 5.4320 5.4366 5.4344 5.4387 5.4365 5.4408 5.4386 5.4429 5.6150 5.6222 5.6184 5.6259 5.6222 5.6297 5.6260 5.6335 5.6600 5.6648 5.6623 5.6673 5.6648 5.6698 5.6673 5.6723 5.6820 5.6866 5.6844 5.6887 5.6865 5.6908 5.6886 5.6929 5.8650 5.8722 5.8684 5.8759 5.8722 5.8797 5.8760 5.8835 5.9100 5.9148 5.9123 5.9173 5.9148 5.9198 5.9173 5.9223 5.9320 5.9366 5.9344 5.9387 5.9365 5.9408 5.9386 5.9429
4 1 ∕ 2 -8 4 1 ∕ 2 -12 4 1 ∕ 2 -16 4 3 ∕ 4 -8 4 3 ∕ 4 -12 4 3 ∕ 4 -16 5-8 5-12 5-16 5 1 ∕ 4 -8 5 1 ∕ 4 -12 5 1 ∕ 4 -16 5 1 ∕ 2 -8 5 1 ∕ 2 -12 5 1 ∕ 2 -16 5 3 ∕ 4 -8 5 3 ∕ 4 -12 5 3 ∕ 4 -16
6-8 6-12 6-16
a This is the minimum minor diameter specified in the thread tables, page 1951. b This is the maximum minor diameter specified in the thread tables, page 1951. All dimensions are in inches. For basis of recommended hole size limits see accompanying text. As an aid in selecting suitable drills, see the listing of American Standard drill sizes starting on page 933 in the twist drill section. For amount of expected drill oversize, see page 962.
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