ISO Metric Thread Tolerance Tables.

The information below can be used to calculate the values of thread tolerances defined by ISO 965/1.

Tolerances are written as a combination of a tolerance band, signified by an alphabetic letter, and a tolerance class, signified by a number. For the tolerance band, uppercase letters (E or G) signify internal threads whilst lowercase letters (e, f, g or h) signify external threads. Grade 6 is an example of a tolerance class which signifies general use, with smaller numbers being used for stricter tolerance and higher numbers being used for more loose tolerances.

For instance, a 5g tolerance for an external thread would signify a tolerance that is in the 5th class of band g (see diagram below for reference).

Screw threads are usually signified by two tolerances. One is for the maximum outside diameter, measured from the major diameter of the thread, and the other is for the pitch diameter, measured from the midpoint of each tooth.

For more information on measuring thread diameters and pitch diameters, please see our article on How To Measure Screws.

As an example, a common screw thread tolerance is 5g6g, which indicates a 5g tolerance on its pitch diameter, and a 6g tolerance on its external (thread) diameter.

Screw threads with identical external tolerances and pitch tolerances are expressed with a single tolerance letter and number. For instance, for a screw with both a 6g major diameter tolerance and a 6g pitch diameter tolerance, this would simply be written as “6g”.

The reason that the values for tolerance bands (signified by letters, found in table 1) are written as positive and negative numbers, and the values for tolerance classes (written as numbers, found in tables 2 - 5) are not, is because tolerance classes are applied interchangeably to both internal and external threads, and must be either subtracted or added to a tolerance, dependent on whether the thread is internal or external.

Important Formulae
D	Major Diameter
D1	Minor Diameter Internal Thread
D2	Pitch Diameter Internal Thread
d	Major Diameter External Thread
d1	Minor Diameter External Thread
d2	Pitch Diameter External Thread
T	Tolerance
T_D1	Tolerance for D1
T_D2	Tolerance for D2
T_d1	Tolerance for d1
T_d2	Tolerance for d2
EI	Lower Deviation Internal Thread
ES	Upper Deviation Internal Thread
ei	Lower Deviation External Thread
es	Upper Deviation External Thread

Important Calculations
Internal Threads
Min major dia.	basic major dia. + EI (Table 1)
Max minor dia.	min minor dia. + T_D1 (Table 2)
Max pitch dia.	min pitch dia. + T_D2 (Table 4)
External Threads
Max major dia.	basic major dia. − es (Table 1)
Min major dia.	max major dia. − T_d (Table 3)
Min pitch dia.	max pitch dia. − T_d2 (Table 5)

Table 1: Fundamental Deviation Codes For Internal and External Metric Threads (EI/es)
Pitch	Allowance (Fundamental Deviation)
	External Thread				Internal Thread
	e	f	g	h	H	G
	es	es	es	es	EI	EI
0.2	N/A	N/A	-0.017	0	0	+0.017
0.25	N/A	N/A	-0.018	0	0	+0.018
0.3	N/A	N/A	-0.018	0	0	+0.018
0.35	N/A	-0.034	-0.019	0	0	+0.019
0.4	N/A	-0.034	-0.019	0	0	+0.019
0.45	N/A	-0.035	-0.020	0	0	+0.020
0.5	-0.050	-0.036	-0.020	0	0	+0.020
0.6	-0.053	-0.036	-0.021	0	0	+0.021
0.7	-0.056	-0.038	-0.022	0	0	+0.022
0.75	-0.056	-0.038	-0.022	0	0	+0.022
0.8	-0.060	-0.038	-0.024	0	0	+0.024
1	-0.060	-0.040	-0.026	0	0	+0.026
1.25	-0.063	-0.042	-0.028	0	0	+0.028
1.5	-0.067	-0.045	-0.032	0	0	+0.032
1.75	-0.071	-0.048	-0.034	0	0	+0.034
2	-0.071	-0.052	-0.038	0	0	+0.038
2.5	-0.080	-0.058	-0.042	0	0	+0.042
3	-0.085	-0.063	-0.048	0	0	+0.048
3.5	-0.090	-0.070	-0.053	0	0	+0.053
4	-0.095	-0.075	-0.060	0	0	+0.060
4.5	-0.100	-0.080	-0.063	0	0	+0.063
5	-0.106	-0.085	-0.071	0	0	+0.071
5.5	-0.112	-0.090	-0.075	0	0	+0.075
6	-0.118	-0.095	-0.080	0	0	+0.080

Table 2: Minor Diameter Tolerance of Internal Metric Threads (T_D1)
Pitch	4	5	6	7	8
0.2	0.038	N/A	N/A	N/A	N/A
0.25	0.045	0.056	N/A	N/A	N/A
0.3	0.053	0.067	0.085	N/A	N/A
0.35	0.063	0.080	0.100	N/A	N/A
0.4	0.071	0.090	0.112	N/A	N/A
0.45	0.080	0.100	0.125	N/A	N/A
0.5	0.090	0.112	0.140	0.180	N/A
0.6	0.100	0.125	0.160	0.200	N/A
0.7	0.112	0.140	0.180	0.224	N/A
0.75	0.118	0.150	0.190	0.236	N/A
0.8	0.125	0.160	0.200	0.250	0.315
1	0.150	0.190	0.236	0.300	0.375
1.25	0.170	0.212	0.265	0.335	0.425
1.5	0.190	0.236	0.300	0.375	0.475
1.75	0.212	0.265	0.335	0.425	0.530
2	0.236	0.300	0.375	0.475	0.600
2.5	0.280	0.355	0.450	0.560	0.710
3	0.315	0.400	0.500	0.630	0.800
3.5	0.355	0.450	0.560	0.710	0.900
4	0.375	0.475	0.600	0.750	0.950
4.5	0.425	0.530	0.670	0.850	1.060
5	0.450	0.560	0.710	0.900	1.120
5.5	0.475	0.600	0.750	0.950	1.180
6	0.500	0.630	0.800	1.000	1.250

Table 3: Major Diameter Tolerance of External Metric Threads (T_d)
Pitch	Tolerance Grade
Pitch	4	6	8
0.2	0.036	0.056	N/A
0.25	0.042	0.067	N/A
0.3	0.048	0.075	N/A
0.35	0.053	0.085	N/A
0.4	0.060	0.095	N/A
0.45	0.063	0.100	N/A
0.5	0.067	0.106	N/A
0.6	0.080	0.125	N/A
0.7	0.090	0.140	N/A
0.75	0.090	0.140	N/A
0.8	0.095	0.150	0.236
1	0.112	0.180	0.280
1.25	0.132	0.212	0.335
1.5	0.150	0.236	0.375
1.75	0.170	0.265	0.425
2	0.180	0.280	0.450
2.5	0.212	0.335	0.530
3	0.236	0.375	0.600
3.5	0.265	0.425	0.670
4	0.300	0.475	0.750
4.5	0.315	0.500	0.800
5	0.335	0.530	0.850
5.5	0.355	0.560	0.900
6	0.375	0.600	0.950

Table 4: Pitch Diameter Tolerance for Internal Metric Threads (T_D2)
Basic Major Diameter		Pitch	Tolerance Grade
Over	Up to and Including	Pitch	4	5	6	7	8
1.5	2.8	0.2	0.042	N/A	N/A	N/A	N/A
		0.25	0.048	0.060	N/A	N/A	N/A
		0.35	0.053	0.067	0.085	N/A	N/A
		0.4	0.056	0.071	0.090	N/A	N/A
		0.45	0.060	0.075	0.095	N/A	N/A
2.8	5.6	0.35	0.056	0.071	0.090	N/A	N/A
		0.5	0.063	0.080	0.100	0.125	N/A
		0.6	0.071	0.090	0.112	0.140	N/A
		0.7	0.075	0.095	0.118	0.150	N/A
		0.75	0.075	0.095	0.118	0.150	N/A
		0.8	0.080	0.100	0.125	0.160	0.200
5.6	11.2	0.75	0.085	0.106	0.132	0.170	N/A
		1	0.095	0.118	0.150	0.190	0.236
		1.25	0.100	0.125	0.160	0.200	0.250
		1.5	0.112	0.140	0.180	0.224	0.280
11.2	22.4	1	0.100	0.125	0.160	0.200	0.250
		1.25	0.112	0.140	0.180	0.224	0.280
		1.5	0.118	0.150	0.190	0.236	0.300
		1.75	0.125	0.160	0.200	0.250	0.315
		2	0.132	0.170	0.212	0.265	0.335
		2.5	0.140	0.180	0.224	0.280	0.355
22.4	45	1	0.106	0.132	0.170	0.212	N/A
		1.5	0.125	0.160	0.200	0.250	0.315
		2	0.140	0.180	0.224	0.280	0.355
		3	0.170	0.212	0.265	0.335	0.425
		3.5	0.180	0.224	0.280	0.355	0.450
		4	0.190	0.236	0.300	0.375	0.475
		4.5	0.200	0.250	0.315	0.400	0.500
45	90	1.5	0.132	0.170	0.212	0.265	0.335
		2	0.150	0.190	0.236	0.300	0.375
		3	0.180	0.224	0.280	0.355	0.450
		4	0.200	0.250	0.315	0.400	0.500
		5	0.212	0.265	0.335	0.425	0.530
		5.5	0.224	0.280	0.355	0.450	0.560
		6	0.236	0.300	0.375	0.475	0.600
90	180	2	0.160	0.200	0.250	0.315	0.400
		3	0.190	0.236	0.300	0.375	0.475
		4	0.212	0.265	0.335	0.425	0.530
		6	0.250	0.315	0.400	0.500	0.630
180	355	3	0.212	0.265	0.335	0.425	0.530
		4	0.236	0.300	0.375	0.475	0.600
		6	0.265	0.335	0.425	0.530	0.670

Table 5: Pitch Diameter Tolerance for External Metric Threads (T_d2)
Basic Major Diameter		Pitch	Tolerance Grade
Over	Up to and Including	Pitch	3	4	5	6	7	8	9
1.5	2.8	0.2	0.025	0.032	0.040	0.050	N/A	N/A	N/A
		0.25	0.028	0.036	0.045	0.056	N/A	N/A	N/A
		0.35	0.032	0.040	0.050	0.063	0.080	N/A	N/A
		0.4	0.034	0.042	0.053	0.067	0.085	N/A	N/A
		0.45	0.036	0.045	0.056	0.071	0.090	N/A	N/A
2.8	5.6	0.35	0.034	0.042	0.053	0.067	0.085	N/A	N/A
		0.5	0.038	0.048	0.060	0.075	0.095	N/A	N/A
		0.6	0.042	0.053	0.067	0.085	0.106	N/A	N/A
		0.7	0.045	0.056	0.071	0.090	0.112	N/A	N/A
		0.75	0.045	0.056	0.071	0.090	0.112	N/A	N/A
		0.8	0.048	0.060	0.075	0.095	0.118	0.150	0.190
5.6	11.2	0.75	0.050	0.063	0.080	0.100	0.125	N/A	N/A
		1	0.056	0.071	0.090	0.112	0.140	0.180	0.224
		1.25	0.060	0.075	0.095	0.118	0.150	0.190	0.236
		1.5	0.067	0.085	0.106	0.132	0.170	0.212	0.265
11.2	22.4	1	0.060	0.075	0.095	0.118	0.150	0.190	0.236
		1.25	0.067	0.085	0.106	0.132	0.170	0.212	0.265
		1.5	0.071	0.090	0.112	0.140	0.180	0.224	0.280
		1.75	0.075	0.095	0.118	0.150	0.190	0.236	0.300
		2	0.080	0.100	0.125	0.160	0.200	0.250	0.315
		2.5	0.085	0.106	0.132	0.170	0.212	0.265	0.335
22.4	45	1	0.063	0.080	0.100	0.125	0.160	0.200	0.250
		1.5	0.075	0.095	0.118	0.150	0.190	0.236	0.300
		2	0.085	0.106	0.132	0.170	0.212	0.265	0.335
		3	0.100	0.125	0.160	0.200	0.250	0.315	0.400
		3.5	0.106	0.132	0.170	0.212	0.265	0.335	0.425
		4	0.112	0.140	0.180	0.224	0.280	0.355	0.450
		4.5	0.118	0.150	0.190	0.236	0.300	0.375	0.475
45	90	1.5	0.080	0.100	0.125	0.160	0.200	0.250	0.315
		2	0.090	0.112	0.140	0.180	0.224	0.280	0.355
		3	0.106	0.132	0.170	0.212	0.265	0.335	0.425
		4	0.118	0.150	0.190	0.236	0.300	0.375	0.475
		5	0.125	0.160	0.200	0.250	0.315	0.400	0.500
		5.5	0.132	0.170	0.212	0.265	0.335	0.425	0.530
		6	0.140	0.180	0.224	0.280	0.355	0.450	0.560
90	180	2	0.095	0.118	0.150	0.190	0.236	0.300	0.375
		3	0.112	0.140	0.180	0.224	0.280	0.355	0.450
		4	0.125	0.160	0.200	0.250	0.315	0.400	0.500
		6	0.150	0.190	0.236	0.300	0.375	0.475	0.600
180	355	3	0.125	0.160	0.200	0.250	0.315	0.400	0.500
		4	0.140	0.180	0.224	0.280	0.355	0.450	0.560
		6	0.160	0.200	0.250	0.315	0.400	0.500	0.630