Tap Tolerance Metric Course & Fine

The ISO metric screw threads are the world-wide most commonly used type of general-purpose screw thread. They were one of the first international standards agreed when the International Organization for Standardization was set up in 1947.  The "M" designation for metric screws indicates the nominal outer diameter of the screw, in millimeters e.g., an M12 screw has a nominal outer diameter of 12 millimeters.

The approved tap tolerance system for metric ISO threads is International Standard ISO 2857.

· 4H tap corresponds to ISO 1
· 6H tap corresponds to ISO 2
· 6G tap corresponds to ISO 3

4H and 6G taps can be supplied upon request. 6G taps are Oversize. Please refer to the Au "G" values table below.

For the special tolerance "7G", an oversize of approx. 2 x Au "G" has been taken into account.

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Tolerance Chart - Metric Coarse / Fine

Metric Coarse Thread	Pitch	Tap Tolerance		Metric Fine Thread (choice)	Tap Tolerance
		4H Tap	6H Tap		4H Tap	6H Tap
M 1.6	0.35	D2	D2 / D3	M 3 x 0.35	D2	D3
M 1.8	0.35	D2	D2 / D3	M 4 x 0.50	D2	D3
M 2.0	0.40	D2	D3	M 6 x 0.50	D2 / D3	D3 / D4
M 2.2	0.45	D2	D3	M 6 x 0.75	D2 / D3	D4
M 2.5	0.45	D2	D3	M 8 x 0.75	D2 / D3	D4
M 3.0	0.50	D2	D3	M 8 x 1.00	D3	D4 / D5
M 3.5	0.60	D2	D3 / D4	M 12 x 1.00	D3	D4 / D5
M 4.0	0.70	D2 / D3	D3 / D4	M 10 x 1.25	D3	D4 / D5
M 4.5	0.75	D2 / D3	D3 / D4	M 14 x 1.25	D3	D4 / D5
M 5.0	0.80	D2 / D3	D3 / D4	M 12 x 1.50	D3 / D4	D5 / D6
M 6.0	1.00	D2 / D3	D4 / D5	M 20 x 1.50	D3 / D4	D5 / D6
M 7.0	1.00	D2 / D3	D4 / D5	M 24 x 1.50	D3 / D4	D5 / D6
M 8.0	1.25	D3	D4 / D5	M 42 x 1.50	D3 / D4	D5 / D6
M 10.0	1.50	D3	D4 / D5	M 18 x 2.00	D3 / D4	D6 / D7
M 12.0	1.75	D3 / D4	D5 / D6	M 24 x 2.00	D4	D6 / D7
M 14.0	2.00	D3 / D4	D5 / D6	M 42 x 2.00	D4	D6 / D7
M 16.0	2.00	D3 / D4	D5 / D6	M 36 x 3.00	D4 / D5	D7 / D8
M 18.0	2.50	D4	D6 / D7	M 42 x 3.00	D4 / D5	D7 / D8
M 20.0	2.50	D4	D6 / D7	M 52 x 3.00	D4 / D5	D7 / D8
M 22.0	2.50	D4	D6 / D7
M 24.0	3.00	D4 / D5	D7 / D8
M 27.0	3.00	D4 / D5	D7 / D8
M 30.0	3.50	D4 / D5	D7 / D8
M 33.0	3.50	D4 / D5	D8 / D9
M 36.0	4.00	D5	D8 / D9
M 39.0	4.00	D5	D8 / D9
M 42.0	4.50	D5	D8 / D9
M 45.0	4.50	D5	D8 / D9
M 48.0	5.00	D5 / D6	D9 / D10
M 52.0	5.00	D5 / D6	D9 / D10

Tolerance Chart - Oversize 6G Taps

Au "G" Values for Oversize Taps "6G Taps"

Pitch	Tap Tolerance
	mm	inch
0.35 - 0.40	0.019	.00075
0.45 - 0.50	0.020	.00079
0.60	0.021	.00083
0.70 - 0.75	0.022	.00087
0.80	0.024	.00094
1.00	0.026	.0010
1.25	0.028	.0011
1.50	0.032	.0013
1.75	0.034	.0013
2.00	0.038	.0015
2.50	0.042	.0017
3.00	0.048	.0019
3.50	0.053	.0021
4.00	0.060	.0024
4.50	0.063	.0025
5.00	0.071	.0028