Tap Recommendations for Classes 2, 3, 2B & 3B

Unified and American Screw Threads

The recommended taps normally 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, a choice of some other limit tap will be necessary.

NUMBERED SIZES

SIZE THREADS PER INCH RECOMMENDED TAP FOR CLASS OF THREAD PITCH DIAMETER LIMITS FOR CLASS OF THREAD
NC NF 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
1 		64 72 GH1
GH1 		GH1
GH1 		GH2
GH2 		GH1
GH1 		.0629
.0640 		.0648
.0658 		.0643
.0653 		.0655
.0665 		.0648
.0659
2
2 		56 64 GH1
GH1 		GH1
GH1 		GH2
GH2 		GH1
GH1 		.0744
.0759 		.0764
.0778 		.0759
.0773 		.0772
.0786 		.0765
.0779
3
3 		48 56 GH1
GH1 		GH1
GH1 		GH2
GH2 		GH1
GH1 		.0855
.0874 		.0877
.0894 		.0871
.0889 		.0885
.0902 		.0877
.0895
4
4 		40 48 GH2
GH1 		GH1
GH1 		GH2
GH2 		GH2
GH1 		.0958
.0985 		.0982
.1007 		.0975
.1001 		.0991
.1016 		.0982
.1008
5
5 		40 44 GH2
GH1 		GH1
GH1 		GH2
GH2 		GH2
GH1 		.1088
.1102 		.1112
.1125 		.1105
.1118 		.1121
.1134 		.1113
.1126
6
6 		32 40 GH2
GH2 		GH1
GH1 		GH3
GH2 		GH2
GH2 		.1177
.1218 		.1204
.1242 		.1196
.1235 		.1214
.1252 		.1204
.1243
8
8 		32 36 GH2
GH2 		GH1
GH1 		GH3
GH2 		GH2
GH2 		.1437
.1460 		.1464
.1485 		.1456
.1478 		.1475
.1496 		.1465
.1487
10
10 		24 32 GH3
GH2 		GH1
GH1 		GH3
GH3 		GH3
GH2 		.1629
.1697 		.1662
.1724 		.1653
.1716 		.1672
.1736 		.1661
.1726
12
12 		24 28 GH3
GH3 		GH1
GH1 		GH3
GH3 		GH3
GH3 		.1889
.1928 		.1922
.1959 		.1913
.1950 		.1933
.1970 		.1922
.1959

FRACTIONAL SIZES

SIZE THREADS PER INCH RECOMME NDED TAP F OR CLASS OF THREAD PITCH DIAMETER L IMITS FOR C LASS OF TH READ
NC AND UNC NF AND UNF CLASS 2 CLASS 3 CLASS 2B CLASS 3B MIN. ALL CLASSES (BASIC) MAX. CLASS 2 MAX. CLASS 3 MAX. CLASS 2B MAX. CLASS 3B
1/4
1/4 		20 28 GH3
GH3 		GH2
GH1 		GH5
GH4 		GH3
GH3 		.2175
.2268 		.2211
.2299 		.2201
.2290 		.2223
.2311 		.2211
.2300
5/16
5/16 		18 24 GH3
GH3 		GH2
GH1 		GH5
GH4 		GH3
GH3 		.2764
.2854 		.2805
.2887 		.2794
.2878 		.2817
.2902 		.2803
.2890
3/8
3/8 		16 24 GH3
GH3 		GH2
GH1 		GH5
GH4 		GH3
GH3 		.3344
.3479 		.3389
.3512 		.3376
.3503 		.3401
.3528 		.3387
.3516
7/16
7/16 		14 20 GH5
GH3 		GH3
GH1 		GH5
GH5 		GH3
GH3 		.3911
.4050 		.3960
.4086 		.3947
.4076 		.3972
.4104 		.3957
.4091
1/2
1/2 		13 20 GH5
GH3 		GH3
GH1 		GH5
GH5 		GH3
GH3 		.4500
.4675 		.4552
.4711 		.4537
.4701 		.4565
.4731 		.4548
.4717
9/16
9/16 		12 18 GH5
GH3 		GH3
GH2 		GH5
GH5 		GH3
GH3 		.5084
.5264 		.5140
.5305 		.5124
.5294

.5152
.5323

.5135
.5308
5/8
5/8 		11 18 GH5
GH3 		GH3
GH2 		GH5
GH5 		GH3
GH3 		.5660
.5889 		.5719
.5930 		.5702
.5919

.5732
.5949

.5714
.5934
3/4
3/4 		10 16 GH5
GH3 		GH3
GH2 		GH5
GH5 		GH5
GH3 		.6850
.7094 		.6914
.7139 		.6895
.7126 		.6927
.7159 		.6907
.7143
7/8
7/8 		9 14 GH6
GH4 		GH4
GH2 		GH6
GH6 		GH4
GH4 		.8028
.8286
.8098
.8335 		.8077
.8322 		.8110
.8356 		.8089
.8339
1
1 		8 12 GH6
GH4 		GH4
GH2 		GH6
GH6 		GH4
GH4 		.9188
.9459 		.9264
.9515 		.9242
.9499 		.9276
.9535 		.9254
.9516
1
14 NS
GH4 GH2 GH6 GH4 .9536 .9585 .9572 .9609 .9590
11/8
11/8 		7 12 GH8
GH4 		GH4
GH4 		GH8
GH6 		GH4
GH4 		1.0322 1.0709 1.0407
1.0765 		1.0381
1.0749 		1.0416
1.0787 		1.0393 1.0768
11/4
11/4 		7 12 GH8
GH4 		GH4
GH4 		GH8
GH6 		GH4
GH4 		1.1572 1.1959 1.1657
1.2015 		1.1631
1.1999 		1.1668
1.2039 		1.1644 1.2019
13/8
13/8 		6 12 GH8
GH4 		GH4
GH4 		GH8
GH6 		GH4
GH4 		1.2667 1.3209 1.2768
1.3265 		1.2738
1.3249 		1.2771
1.3291 		1.2745 1.3270
11/2
11/2 		6 12 GH8
GH4 		GH4
GH4 		GH8
GH6 		GH4
GH4 		1.3917 1.4459 1.4018
1.4515 		1.3988
1.4499 		1.4022
1.4542 		1.3996 1.4522