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 |