Tap Tolerance UNC/UNCF

The tolerance of the tap should be manufactured as close as possible to the finished internal thread tolerance.

This practice ensures that the threads produced will comply to the gage tolerances providing that the working conditions such as machine, chucking tools, and workpiece match the application.

Taps are general marked with the appropriate tolerance class for their intended use. The U.S. GH thread class numbers are not marked on the tap.

Tolerances for the various GH numbers are shown in the chart opposite.

Classification for the tolerance 1B can be provided upon request.

Taps for cast iron and titanium tapping are designed one GH class higher to provide better tool life.

UNC Thread	Tap Limit		UNF Thread	Tap Limit
	3B (Tap)	2B (Tap)		3B (Tap)	2B (Tap)
No. 1 - 64	H1 / H2	H2 / H3	No. 0 - 80	H1	H1 / H2
No. 2 - 56	H1 / H2	H2 / H3	No. 1 - 72	H1 / H2	H2 / H3
No. 3 - 48	H1 / H2	H2 / H3	No. 2 - 64	H1 / H2	H2 / H3
No. 4 - 40	H2	H2 / H3	No. 3 - 56	H1 / H2	H2 / H3
No. 5 - 40	H2	H2 / H3	No. 4 - 48	H2	H2 / H3
No. 6 - 32	H2	H3 / H4	No. 5 - 44	H2	H2 / H3
No. 8 - 32	H2	H3 / H4	No. 6 - 40	H2	H2 / H3
No. 10 - 24	H2 / H3	H3 / H4	No. 8 - 36	H2	H2 / H3
No. 12 - 24	H2 / H3	H3 / H4	No. 10 - 32	H2	H2 / H3
1/4 - 20	H3	H4 / H5	No. 12 - 28	H2 / H3	H3 / H4
5/16 - 18	H3	H4 / H5	1/4 - 28	H2 / H3	H3 / H4
3/8 - 16	H3 / H4	H4 / H5	5/16 - 24	H3	H3 / H4
7/16 - 14	H3 / H4	H4 / H5	3/8 - 24	H3	H3 / H4
1/2 - 13	H4	H5 / H6	7/16 - 20	H3	H4 / H5
9/16 - 12	H4	H5 / H6	1/2 - 20	H3	H4 / H5
5/8 - 11	H4	H5 / H6	9/16 - 18	H3 / H4	H4 / H5
3/4 - 10	H4 / H5	H6 / H7	5/8 - 18	H3 / H4	H5 / H6
7/8 - 9	H4 / H5	H6 / H7	3/4 - 16	H4	H5 / H6
1 - 8	H5	H6 / H7	7/8 - 14	H4	H5 / H6
1 1/8 - 7	H5	H7 / H8	1 - 12	H4 / H5	H5 / H6
1 1/4 - 7	H5 / H6	H7 / H8	1 1/8 - 12	H4 / H5	H6 / H7
1 3/8 - 6	H6	H7 / H8	1 1/4 - 12	H4 / H5	H6 / H7
1 1/2 - 6	H6	H7 / H8	1 3/8 - 12	H4 / H5	H6 / H7
1 3/4 - 5	H6 / H7	H8 / H9	1 1/12 - 12	H4 / H5	H6 / H7
2 - 4 1/2	H7	H8 / H9