Table 3. Standard Series and Selected Combinations—Unified Screw Threads Table 3. (Continued) Standard Series and Selected Combinations—Unified Screw Threads
External b
Internal b
Nominal Size, Threads per Inch, and Series Designation a
Major Diameter
UNR Minor Dia., c Max (Ref.)
Major Diameter
Pitch Diameter
Minor Diameter
Pitch Diameter
Allow ance
Max d
Min e
Max d
Class
Min
Min
Min
Max
Min
Max
Min 2.6250 2.6250 2.7500 2.7500 2.7500 2.7500 2.7500 2.7500 2.7500 2.7500 2.7500 2.7500 2.7500 2.7500 2.7500 2.7500 2.7500 2.7500 2.8750 2.8750 2.8750 2.8750 2.8750 2.8750 2.8750 2.8750 2.8750 2.8750
Class
2A 0.0015 2.6235 2.6154 3A 0.0000 2.6250 2.6169 1A 0.0032 2.7468 2.7111 3A 0.0000 2.7500 2.7262 2A 0.0027 2.7473 2.7291 3A 0.0000 2.7500 2.7318 3A 0.0000 2.7500 2.7350 2A 0.0020 2.7480 2.7351 2A 0.0019 2.7481 2.7367 3A 0.0000 2.7500 2.7386 2A 0.0018 2.7482 2.7379 2A 0.0017 2.7483 2.7389 3A 0.0000 2.7500 2.7406 2A 0.0016 2.7484 2.7397 2A 0.0015 2.7485 2.7404 3A 0.0000 2.7500 2.7419 2A 0.0028 2.8722 2.8540 3A 0.0000 2.8750 2.8568 2A 0.0025 2.8725 2.8575 3A 0.0000 2.8750 2.8600 2A 0.0019 2.8731 2.8617 3A 0.0000 2.8750 2.8636 2A 0.0017 2.8733 2.8639 3A 0.0000 2.8750 2.8656 2A 0.0016 2.8734 2.8653 3A 0.0000 2.8750 2.8669
— 2.5910 2.5859 — 2.5925 2.5887 — 2.5844 2.5686 — 2.5876 2.5797 — 2.6390 2.6299 — 2.6417 2.6349 — 2.6688 2.6625 — 2.6830 2.6762 — 2.6940 2.6877 — 2.6959 2.6912 — 2.7018 2.6959 — 2.7077 2.7021 — 2.7094 2.7052 — 2.7123 2.7070 — 2.7160 2.7109 — 2.7175 2.7136 — 2.7639 2.7547 — 2.7667 2.7598 — 2.7913 2.7829 — 2.7938 2.7875 — 2.8190 2.8127 — 2.8209 2.8162 — 2.8327 2.8271 — 2.8344 2.8302 — 2.8409 2.8357 — 2.8425 2.8386
2.5640 2.5655 2.4491 2.4491 2.4523 2.5488 2.5515 2.5987 2.6012 2.6289 2.6489 2.6508 2.6631 2.6739 2.6756 2.6822 2.6890 2.6905 2.6737 2.6765 2.7237 2.7262 2.7739 2.7758 2.7989 2.8006 2.8139 2.8155
2B 2.571
2.582
2.5925 2.5991 2.5925 2.5975 2.5876 2.6082 2.5876 2.6013 2.5876 2.5979 2.6417 2.6536 2.6417 2.6506 2.6688 2.6796 2.6688 2.6769 2.6850 2.6938 2.6959 2.7040 2.6959 2.7020 2.7036 2.7113 2.7094 2.7167 2.7094 2.7148 2.7139 2.7209 2.7175 2.7242 2.7175 2.7225 2.7667 2.7787 2.7667 2.7757 2.7938 2.8048 2.7938 2.8020 2.8209 2.8291 2.8209 2.8270 2.8344 2.8417 2.8344 2.8399 2.8425 2.8492 2.8425 2.8475
2 5 ∕ 8 -20 UN
3B 2.5710 2.5786
1B 2.479 2B 2.479
2.517 2.517
2 3 ∕ 4 -4 UNC
2A 0.0032 2.7468 2.7230 2.7111 2.5844 2.5739
3B 2.4790 2.5094
2B 2.570
2.600
2 3 ∕ 4 -6 UN
3B 2.5700 2.5896
2A 0.0025 2.7475 2.7325 2.7250 2.6663 2.6580
2B 2.615
2.640
2 3 ∕ 4 -8 UN
3B 2.6150 2.6297
2B 2.642 2B 2.660 2B 2.673 2B 2.682 2B 2.690 2B 2.696
2.663 2.678 2.688 2.696 2.703 2.707
2 3 ∕ 4 -10 UNS 2 3 ∕ 4 -12 UN 2 3 ∕ 4 -14 UNS 2 3 ∕ 4 -16 UN 2 3 ∕ 4 -18 UNS 2 3 ∕ 4 -20 UN
3B 2.6600 2.6698
3B 2.6820 2.6909
3B 2.6960 2.7036
2B 2.695
2.725
2 7 ∕ 8 -6 UN
3B 2.6950 2.7146
2B 2.740
2.765
2 7 ∕ 8 -8 UN
3B 2.7400 2.7547
2B 2.785
2.803
2 7 ∕ 8 -12 UN
3B 2.7850 2.7948
2B 2.807
2.821
2 7 ∕ 8 -16 UN
3B 2.8070 2.8159
2B 2.821
2.832
2 7 ∕ 8 -20 UN
3B 2.8210 2.8286
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