External Screw Threads Size and Tolerances

Author: Scott Bredemann

Updated: 03/24/2025 | Read Time: 3mins

The American National Standards Institute (ANSI) sets guidelines for external screw threads, specifying dimensions and tolerances based on thread class (2A and 3A). These standards help engineers and manufacturers maintain consistency, reduce wear, and improve performance across various industrial and commercial uses.

This guide provides a detailed table of ANSI external screw thread sizes, covering major, pitch, and minor diameters along with their tolerances.

Screw Size	Thread Class	Major Diameter	Major Diameter	Major Diameter	Pitch Diameter	Pitch Diameter	Minor Diameter
		Basic	Max	Min	Max	Min	Min
0-80	2A	0.06	0.0605	0.0595	0.0518	0.0506	0.0455
0-80	3A	0.06	0.0603	0.0597	0.0523	0.0511	0.0458
1-64	2A	0.073	0.0735	0.0725	0.0638	0.0626	0.0565
1-64	3A	0.073	0.0733	0.0727	0.0642	0.063	0.0568
1-72	2A	0.073	0.0735	0.0725	0.0648	0.0636	0.0574
1-72	3A	0.073	0.0733	0.0727	0.0652	0.064	0.0577
2-56	2A	0.086	0.0865	0.0855	0.0766	0.0754	0.069
2-56	3A	0.086	0.0863	0.0857	0.077	0.0758	0.0693
2-64	2A	0.086	0.0865	0.0855	0.0776	0.0764	0.07
2-64	3A	0.086	0.0863	0.0857	0.078	0.0768	0.0703
3-48	2A	0.099	0.0995	0.0985	0.0893	0.0881	0.0813
3-48	3A	0.099	0.0993	0.0987	0.0897	0.0885	0.0816
3-56	2A	0.099	0.0995	0.0985	0.0903	0.0891	0.0823
3-56	3A	0.099	0.0993	0.0987	0.0907	0.0895	0.0826
4-40	2A	0.112	0.1125	0.1115	0.1008	0.0996	0.0919
4-40	3A	0.112	0.1123	0.1117	0.1012	0.1	0.0922
4-48	2A	0.112	0.1125	0.1115	0.1023	0.1011	0.0934
4-48	3A	0.112	0.1123	0.1117	0.1027	0.1015	0.0937
5-40	2A	0.125	0.1255	0.1245	0.1133	0.1121	0.1039
5-40	3A	0.125	0.1253	0.1247	0.1137	0.1125	0.1042
5-44	2A	0.125	0.1255	0.1245	0.1143	0.1131	0.1049
5-44	3A	0.125	0.1253	0.1247	0.1147	0.1135	0.1052
6-32	2A	0.138	0.1389	0.1369	0.1228	0.1209	0.107
6-32	3A	0.138	0.1386	0.1372	0.1232	0.1213	0.1073
6-40	2A	0.138	0.1389	0.1369	0.125	0.1231	0.1111
6-40	3A	0.138	0.1386	0.1372	0.1254	0.1235	0.1114
8-32	2A	0.164	0.1649	0.1629	0.1483	0.1464	0.1329
8-32	3A	0.164	0.1646	0.1632	0.1487	0.1468	0.1332
8-36	2A	0.164	0.1649	0.1629	0.1501	0.1482	0.1351
8-36	3A	0.164	0.1646	0.1632	0.1505	0.1486	0.1354
10-24	2A	0.19	0.1909	0.1889	0.1683	0.1664	0.1497
10-24	3A	0.19	0.1906	0.1892	0.1687	0.1668	0.15
10-32	2A	0.19	0.1909	0.1889	0.1749	0.173	0.1582
10-32	3A	0.19	0.1906	0.1892	0.1753	0.1734	0.1585
1/4-20	2A	0.25	0.2511	0.2489	0.2263	0.2238	0.2019
1/4-20	3A	0.25	0.2508	0.2492	0.2267	0.2242	0.2022
1/4-28	2A	0.25	0.2511	0.2489	0.2338	0.2313	0.2128
1/4-28	3A	0.25	0.2508	0.2492	0.2342	0.2317	0.2131
5/16-18	2A	0.3125	0.3138	0.3112	0.2832	0.2805	0.256
5/16-18	3A	0.3125	0.3135	0.3115	0.2836	0.2809	0.2563
5/16-24	2A	0.3125	0.3138	0.3112	0.2912	0.2885	0.2663
5/16-24	3A	0.3125	0.3135	0.3115	0.2916	0.2889	0.2666
3/8-16	2A	0.375	0.3765	0.3735	0.3401	0.3372	0.3082
3/8-16	3A	0.375	0.3762	0.3738	0.3405	0.3376	0.3085
3/8-24	2A	0.375	0.3765	0.3735	0.3485	0.3456	0.3192
3/8-24	3A	0.375	0.3762	0.3738	0.3489	0.346	0.3195
7/16-14	2A	0.4375	0.4392	0.4358	0.3963	0.3931	0.3595
7/16-14	3A	0.4375	0.4384	0.4366	0.3968	0.3937	0.3598
7/16-20	2A	0.4375	0.4392	0.4358	0.4108	0.408	0.3787
7/16-20	3A	0.4375	0.4384	0.4366	0.4113	0.4085	0.379
1/2-13	2A	0.5	0.502	0.4976	0.4531	0.4497	0.4099
1/2-13	3A	0.5	0.5012	0.4988	0.4537	0.4503	0.4102
1/2-20	2A	0.5	0.502	0.4976	0.4714	0.4686	0.4402
1/2-20	3A	0.5	0.5012	0.4988	0.4719	0.4691	0.4405
9/16-12	2A	0.5625	0.5648	0.5602	0.5096	0.5059	0.4606
9/16-12	3A	0.5625	0.5638	0.5612	0.5102	0.5065	0.4609
9/16-18	2A	0.5625	0.5648	0.5602	0.5258	0.523	0.4971
9/16-18	3A	0.5625	0.5638	0.5612	0.5263	0.5235	0.4974
5/8-11	2A	0.625	0.6275	0.6225	0.5676	0.5636	0.5149
5/8-11	3A	0.625	0.6264	0.6236	0.5682	0.5642	0.5152
5/8-18	2A	0.625	0.6275	0.6225	0.588	0.585	0.556
5/8-18	3A	0.625	0.6264	0.6236	0.5885	0.5855	0.5563
3/4-10	2A	0.75	0.7528	0.7472	0.6825	0.678	0.6151
3/4-10	3A	0.75	0.7516	0.7484	0.6831	0.6786	0.6154
3/4-16	2A	0.75	0.7528	0.7472	0.7139	0.7109	0.6781
3/4-16	3A	0.75	0.7516	0.7484	0.7144	0.7114	0.6784
7/8-9	2A	0.875	0.878	0.872	0.7977	0.7927	0.7185
7/8-9	3A	0.875	0.8767	0.8733	0.7983	0.7933	0.7188
7/8-14	3A	0.875	0.8767	0.8733	0.8343	0.8311	0.7965
1-8	2A	1	1.003	0.997	0.9074	0.9024	0.8186
1-8	3A	1	1.0017	0.9983	0.908	0.903	0.8189
1-12	2A	1	1.003	0.997	0.949	0.944	0.8696
1-12	3A	1	1.0017	0.9983	0.9495	0.9445	0.8699
1-1/8-7	2A	1.125	1.1285	1.1215	1.0474	1.0416	0.9486
1-1/8-12	2A	1.125	1.1285	1.1215	1.0739	1.0689	0.9936
1-3/8-6	2A	1.375	1.379	1.371	1.2899	1.2833	1.1816
1-3/8-12	2A	1.375	1.379	1.371	1.3239	1.3189	1.2436
1-1/2-6	2A	1.5	1.504	1.496	1.4149	1.4083	1.3066
1-1/2-12	2A	1.5	1.504	1.496	1.4489	1.4439	1.3686
1-3/4-5	2A	1.75	1.7544	1.7456	1.656	1.6484	1.5352
2-6	2A	2	2.004	1.996	1.9149	1.9083	1.8066

Conclusion

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