Industrial Catalog
Classes of Fit
For Classes 2, 3, 1B, 2B and 3B Unified and American National Screw Threads
THREADS PER INCH
RECOMMENDED TAP LIMITS
INTERNAL THREAD PITCH DIAMETER LIMITS
Min. /All Classes (Basic)
Max Class 2B
NC UNC
NF UNF
.0536 .0648 .0658 .0764 .0778 .0877 .0894 .0982 .1007 .1112 .1125 .1204 .1242 .1464 .1485 .1662 .1724 .1922 .1959 .2211 .2299 .2805 .2887 .3389 .3512 .3960 .4086 .4552 .4711 .5140 .5305 .5719 .5930 .6914 .7139 .8098 .8335 .9264 .9515 .9585 Max Class 2 1.0407 1.0765 1.1657 1.2015 1.2768 1.3265 1.4018 1.4515
.0532 .0643 .0653 .0759 .0773 .0871 .0889 .0975 .1001 .1105 .1118 .1196 .1235 .1456 .1478 .1653 .1716 .1913 .1950 .2201 .2290 .2794 .2878 .3376 .3503 .3947 .4076 .4537 .4701 .5124 .5294 .5702 .5919 .6895 .7126 .8077 .8322 .9242 .9499 .9572 Max Class 3 1.0381 1.0749 1.1631 1.1999 1.2738 1.3249 1.3988 1.4499
Max Class 3B
Size
Class 2B Class 3B
G H1 G H1 G H1 G H1 G H1 G H1 G H1 G H2 G H1 G H2 G H1 G H2 G H2 G H2 G H2 G H3 G H2 G H3 G H3 G H3 G H3 G H3 G H3 G H3 G H3 G H5 G H3 G H5 G H3 G H5 G H3 G H5 G H3 G H5 G H3 G H6 G H4 G H6 G H4 G H4 G H8 G H4 G H8 G H4 G H8 G H4 G H8 G H4 Class 2
G H1 G H1 G H1 G H1 G H1 G H1 G H1 G H1 G H1 G H1 G H1 G H1 G H1 G H1 G H1 G H1 G H1 G H1 G H1 G H2 G H1 G H2 G H1 G H2 G H1 G H3 G H1 G H3 G H1 G H3 G H2 G H3 G H2 G H3 G H2 G H4 G H2 G H4 G H2 G H2 G H4 G H4 G H4 G H4 G H4 G H4 G H4 G H4 Class 3
0 1 1 2 2 3 3 4 4 5 5 6 6 8 8
80
G H2 G H2 G H2 G H2 G H2 G H2 G H2 G H2 G H2 G H2 G H2 G H3 G H2 G H3 G H2 G H3 G H3 G H3 G H3 G H5 G H4 G H5 G H4 G H5 G H4 G H5 G H5 G H5 G H5 G H5 G H5 G H5 G H5 G H5 G H5 G H6 G H6 G H6 G H6 G H6 G H8 G H6 G H8 G H6 G H8 G H6 G H8 G H6
G H1 G H1 G H1 G H1 G H1 G H1 G H1 G H2 G H1 G H2 G H1 G H2 G H2 G H2 G H2 G H3 G H2 G H3 G H3 G H3 G H3 G H3 G H3 G H3 G H3 G H3 G H3 G H3 G H3 G H3 G H3 G H3 G H3 G H5 G H3 G H4 G H4 G H4 G H4 G H4 G H4 G H4 G H4 G H4 G H4 G H4 G H4 G H4
.0519 .0629 .0640 .0744 .0759 .0855 .0874 .0958 .0985 .1088 .1102 .1177 .1218 .1437 .1460 .1629 .1697 .1889 .1928 .2175 .2268 .2764 .2854 .3344 .3479 .3911 .4050 .4500 .4675 .5084 .5264 .5660 .5889 .6850 .7094 .8028 .8286 .9188 .9459 .9536
.0542 .0655 .0665 .0772 .0786 .0885 .0902 .0991 .1016 .1121 .1134 .1214 .1252 .1475 .1496 .1672 .1736 .1933 .1970 .2223 .2311 .2817 .2902 .3401 .3528 .3972 .4104 .4565 .4731 .5152 .5323 .5732 .5949 .6927 .7159 .8110 .8356 .9276 .9535 .9609
.0536 .0648 .0659 .0765 .0779 .0877 .0895 .0982 .1008 .1113 .1126 .1204 .1243 .1465 .1487 .1661 .1726 .1922 .1959 .2211 .2300 .2803 .2890 .3387 .3516 .3957 .4091 .4548 .4717 .5135 .5308 .5714 .5934 .6907 .7143 .8089 .8339 .9254 .9516 .9590
64
72
56
64
48
56
40
48
40
44
32
40
32
36
10 10 12 12
24
32
24
28
1/4 1/4
20
28
5/16 5/16
18
Classes of Fit
24
3/8 3/8
16
24
7/16 7/16
14
20
1/2 1/2
13
20
9/16 9/16
12
18
5/8 5/8 3/4 3/4 7/8 7/8
11
18
10
16
9
14
1 1
8
12
1 14 NS
1-1/8 1-1/8 1-1/4 1-1/4 1-3/8 1-3/8 1-1/2 1-1/2
7
1.0322 1.0709 1.1572 1.1959 1.2667 1.3209 1.3917 1.4459
1.0416 1.0787 1.1668 1.2039 1.2771 1.3291 1.4022 1.4542
1.0393 1.0768 1.1644 1.2019 1.2745 1.3270 1.3996 1.4522
12
7
12
6
12
6
12
NOTES: Class 1B: Tapped holes can be produced with cut thread taps. Class 2B: Cut thread taps may be used under normal conditions and in average materials for producing tapped holes to this classification. The above 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. 13
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