Tap Recommendations for Classes of Thread
Unified and American National Screw Threads

this page is for information only

Nominal
Size
T.P.I.
NC
UNC
T.P.I.
NF
UNF
Recommended Tap
for Class of Thread
Pitch Diameter Limits
for Class of Thread
Class
2
Class
3
Class
2B
Class
3B
Min.
All Classes
(Basic)
Max.
Class 2
Max.
Class 3
Max.
Class 2B
Max.
Class 3B
0   80 GH1 GH1 GH2 GH1 .0519 .0536 .0532 .0542 .0536
1 64   GH1 GH1 GH2 GH1 .0629 .0648 .0643 .0655 .0648
1   72 GH1 GH1 GH2 GH1 .0640 .0658 .0653 .0665 .0659
2 56   GH1 GH1 GH2 GH1 .0744 .0764 .0759 .0772 .0765
2   64 GH1 GH1 GH2 GH1 .0759 .0778 .0773 .0786 .0779
3 48   GH1 GH1 GH2 GH1 .0855 .0877 .0871 .0885 .0877
3   56 GH1 GH1 GH2 GH1 .0874 .0894 .0889 .0902 .0895
4 40   GH2 GH1 GH2 GH2 .0958 .0982 .0975 .0991 .0982
4   48 GH1 GH1 GH2 GH1 .0985 .1007 .1001 .1016 .1008
5 40   GH2 GH1 GH2 GH2 .1088 .1112 .1105 .1121 .1113
5   44 GH1 GH1 GH2 GH1 .1102 .1125 .1118 .1134 .1126
6 32   GH2 GH1 GH3 GH2 .1177 .1204 .1196 .1214 .1204
6   40 GH2 GH1 GH2 GH2 .1218 .1242 .1235 .1252 .1243
8 32   GH2 GH1 GH3 GH2 .1437 .1464 .1456 .1475 .1465
8   36 GH2 GH1 GH2 GH2 .1460 .1485 .1478 .1496 .1487
10 24   GH3 GH1 GH3 GH3 .1629 .1662 .1653 .1672 .1661
10   32 GH2 GH1 GH3 GH2 .1697 .1724 .1716 .1736 .1726
12 24   GH3 GH1 GH3 GH3 .1889 .1922 .1913 .1933 .1922
12   28 GH3 GH1 GH3 GH3 .1928 .1959 .1950 .1970 .1959
1/4 20   GH3 GH2 GH5 GH3 .2175 .2211 .2201 .2223 .2211
1/4   28 GH3 GH1 GH4 GH3 .2268 .2299 .2290 .2311 .2300
5/16 18   GH3 GH2 GH5 GH3 .2764 .2805 .2794 .2817 .2803
5/16   24 GH3 GH1 GH4 GH3 .2854 .2887 .2878 .2902 .2890
3/8 16   GH3 GH2 GH5 GH3 .3344 .3389 .3376 .3401 .3387
3/8   24 GH3 GH1 GH4 GH3 .3479 .3512 .3503 .3528 .3516
7/16 14   GH5 GH3 GH5 GH3 .3911 .3960 .3947 .3972 .3957
7/16   20 GH3 GH1 GH5 GH3 .4050 .4086 .4076 .4104 .4091
1/2 13   GH5 GH3 GH5 GH3 .4500 .4552 .4537 .4565 .4548
1/2   20 GH3 GH1 GH5 GH3 .4675 .4711 .4701 .4731 .4717
9/16 12   GH5 GH3 GH5 GH3 .5084 .5140 .5124 .5152 .5135
9/16   18 GH3 GH2 GH5 GH3 .5264 .5305 .5294 .5323 .5308
5/8 11   GH5 GH3 GH5 GH3 .5660 .5719 .5702 .5732 .5714
5/8   18 GH3 GH2 GH5 GH3 .5889 .5930 .5919 .5949 .5934
3/4 10   GH5 GH3 GH5 GH5 .6850 .6914 .6895 .6927 .6907
3/4   16 GH3 GH2 GH5 GH3 .7094 .7139 .7126 .7159 .7143
7/8 9   GH6 GH4 GH6 GH4 .8028 .8098 .8077 .8110 .8089
7/8   14 GH4 GH2 GH6 GH4 .8286 .8335 .8322 .8356 .8339
1 8   GH6 GH4 GH6 GH4 .9188 .9264 .9242 .9276 .9254
1   12 GH4 GH2 GH6 GH4 .9459 .9515 .9499 .9535 .9516
1   14* GH4 GH2 GH6 GH4 .9536 .9585 .9572 .9609 .9590
1 1/8 7   GH8 GH4 GH8 GH4 1.0322 1.0407 1.0381 1.0416 1.0393
1 1/8   12 GH4 GH4 GH6 GH4 1.0709 1.0765 1.0749 1.0787 1.0768
1 1/4 7   GH8 GH4 GH8 GH4 1.1572 1.1657 1.1631 1.1668 1.1644
1 1/4   12 GH4 GH4 GH6 GH4 1.1959 1.2015 1.1999 1.2039 1.2019
1 3/8 6   GH8 GH4 GH8 GH4 1.2667 1.2768 1.2738 1.2771 1.2745
1 3/8   12 GH4 GH4 GH6 GH4 1.3209 1.3265 1.3249 1.3291 1.3270
1 1/2 6   GH8 GH4 GH8 GH4 1.3917 1.4018 1.3988 1.4022 1.3996
1 1/2   12 GH4 GH4 GH6 GH4 1.4459 1.4515 1.4499 1.4542 1.4522

*UN
These are general tap recommendations to produce the Class of Thread indicated in average materials when used with reasonable care. However, if the tap specified does not give a satisfactory gage fit in the work, please consult the factory.

 

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