Special Taps and Dies

Special Taps and DiesCommercial Ground Thread - American National Form

The following tables and formulae are used in determining the limits and tolerances for ground thread taps having special diameter or special pitch or both. Lead Tolerance...a maximum lead error of plus or minus 0.0005 inch in one inch of thread is permitted.

Angle Tolerance:

Threads per inch	Error in Half Angle
4 to 5 1/2 incl.	20' plus or minus
6 to 9 incl.	25' plus or minus
10 to 56 incl.	30' plus or minus

Formulae:

A = Major Diameter Tolerance
B = Amount over basic for minimum pitch diameter
C = A constant to add:
35% of the theoretical truncation for 4 to 5 threads per inch
40% for 5 1/2 to 12 threads per inch
45% for 13 to 56 threads per inch.
To nearest 0.005 inch for 8 or more threads per inch and to nearest 0.001 inch for less than 8 threads per inch.
D = Pitch diameter tolerance:
Maximum Major Diameter = Basic plus C
Minimum Major Diameter = Maximum minus A
Maximum Pitch Diameter = Minimum plus D
Minimum Pitch Diameter = Basic plus B

Values for A, B, C, and D:

		B
Threads per inch	A	to 3/4 inch incl.	Over 3/4 inch to 1 1/2 inch incl.	Over 1 1/2 inch to 2 1/4 inch incl.	Over 2 1/4 inch	C	D
56	0.0010	0.0002	0.0010	0.0015	0.0020	0.0015	0.0010
48	0.0010	0.0002	0.0010	0.0015	0.0020	0.0020	0.0010
44	0.0010	0.0002	0.0010	0.0015	0.0020	0.0020	0.0010
40	0.0010	0.0002	0.0010	0.0015	0.0020	0.0025	0.0010
36	0.0010	0.0002	0.0010	0.0015	0.0020	0.0025	0.0010
32	0.0010	0.0005	0.0010	0.0015	0.0020	0.0030	0.0010
28	0.0010	0.0005	0.0010	0.0015	0.0020	0.0035	0.0010
24	0.0010	0.0005	0.0010	0.0015	0.0020	0.0040	0.0010
20	0.0010	0.0005	0.0010	0.0015	0.0020	0.0050	0.0010
18	0.0010	0.0005	0.0010	0.0015	0.0020	0.0055	0.0010
16	0.0010	0.0005	0.0010	0.0015	0.0020	0.0060	0.0010
14	0.0010	0.0005	0.0010	0.0015	0.0020	0.0070	0.0010
13	0.0010	0.0005	0.0010	0.0015	0.0020	0.0075	0.0010
12	0.0010	0.0005	0.0010	0.0015	0.0020	0.0075	0.0010
11	0.0010	0.0005	0.0010	0.0015	0.0020	0.0080	0.0011
10	0.0015	0.0005	0.0010	0.0015	0.0020	0.0090	0.0011
9	0.0015	....	0.0010	0.0015	0.0020	0.0100	0.0012
8	0.0015	....	0.0010	0.0015	0.0020	0.0110	0.0014
7	0.0020	....	0.0010	0.0015	0.0020	0.0120	0.0015
6	0.0020	....	0.0010	0.0015	0.0020	0.0140	0.0018
5 1/2	0.0025	....	....	0.0015	0.0020	0.0160	0.0020
5	0.0025	....	....	0.0015	0.0020	0.0160	0.0020
4 1/2	0.0025	....	....	0.0015	0.0020	0.0170	0.0020
4	0.0025	....	....	0.0015	0.0020	0.0190	0.0020