The following table defines recommended industry standard sizes for External ACME General Purpose Threads per American National Standard ASME/ANSI B1.5.
There are three classes of General Purpose ACME threads, 2G, 3G, and 4G each class provides some clearance on all standard size diameters for free movement, and are used in assemblies with the internal thread rigidly fixed and movement of the external thread in a direction perpendicular to its axis limited by its bearing or bearings.
Designs should only utilize external and internal ACME threads of the same class and type, with Class 2G being the preferred choice. If less backlash or end play is desired, Classes 3G and 4G are provided. Class 5G is not recommended for new designs.
|
Designation
|
Size Decimal
|
TPI
|
Tol. Class
|
Major Dia.
|
Pitch Dia.
|
Minor Dia.
|
|||
|
Max.
|
Min.
|
Max.
|
Min.
|
Max
|
Min.
|
||||
|
1/4-16 Acme
|
0.25
|
16
|
2G
|
0.2500
|
0.2450
|
0.2148
|
0.2043
|
0.1775
|
0.1618
|
|
1/4-16 Acme
|
0.25
|
16
|
3G
|
0.2500
|
0.2450
|
0.2158
|
0.2109
|
0.1775
|
0.1702
|
|
1/4-16 Acme
|
0.25
|
16
|
4G
|
0.2500
|
0.2450
|
0.2168
|
0.2133
|
0.1775
|
0.1722
|
|
1/4-16 Acme
|
0.25
|
16
|
5G
|
0.2500
|
0.2450
|
0.2188
|
0.2160
|
0.1775
|
0.1733
|
|
5/16-14 Acme
|
0.3125
|
14
|
2G
|
0.3125
|
0.3075
|
0.2728
|
0.2614
|
0.2311
|
0.2140
|
|
5/16-14 Acme
|
0.3125
|
14
|
3G
|
0.3125
|
0.3075
|
0.2738
|
0.2685
|
0.2311
|
0.2231
|
|
5/16-14 Acme
|
0.3125
|
14
|
4G
|
0.3125
|
0.3075
|
0.2748
|
0.271
|
0.2311
|
0.2254
|
|
5/16-14 Acme
|
0.3125
|
14
|
5G
|
0.3125
|
0.3075
|
0.2768
|
0.2738
|
0.2311
|
0.2266
|
|
3/8-12 Acme
|
0.375
|
12
|
2G
|
0.3750
|
0.3700
|
0.3284
|
0.3161
|
0.2817
|
0.2632
|
|
3/8-12 Acme
|
0.375
|
12
|
3G
|
0.3750
|
0.3700
|
0.3296
|
0.3238
|
0.2817
|
0.2730
|
|
3/8-12 Acme
|
0.375
|
12
|
4G
|
0.3750
|
0.3700
|
0.3309
|
0.3268
|
0.2817
|
0.2755
|
|
3/8-12 Acme
|
0.375
|
12
|
5G
|
0.3750
|
0.3700
|
0.3333
|
0.33
|
0.2817
|
0.2767
|
|
7/16-12 Acme
|
0.4375
|
12
|
2G
|
0.4375
|
0.4325
|
0.3909
|
0.3783
|
0.3442
|
0.3253
|
|
7/16-12 Acme
|
0.4375
|
12
|
3G
|
0.4375
|
0.4325
|
0.3921
|
0.3862
|
0.3442
|
0.3354
|
|
7/16-12 Acme
|
0.4375
|
12
|
4G
|
0.4375
|
0.4325
|
0.3934
|
0.3892
|
0.3442
|
0.3379
|
|
7/16-12 Acme
|
0.4375
|
12
|
5G
|
0.4375
|
0.4325
|
0.3958
|
0.3924
|
0.3442
|
0.3391
|
|
1/2-10 Acme
|
0.5
|
10
|
2G
|
0.5000
|
0.4950
|
0.4443
|
0.4306
|
0.3800
|
0.3594
|
|
1/2-10 Acme
|
0.5
|
10
|
3G
|
0.5000
|
0.4950
|
0.4458
|
0.4394
|
0.3800
|
0.3704
|
|
1/2-10 Acme
|
0.5
|
10
|
4G
|
0.5000
|
0.4950
|
0.4472
|
0.4426
|
0.3800
|
0.3731
|
|
1/2-10 Acme
|
0.5
|
10
|
5G
|
0.5000
|
0.4950
|
0.45
|
0.4463
|
0.3800
|
0.3745
|
|
5/8-8 Acme
|
0.625
|
8
|
2G
|
0.6250
|
0.6188
|
0.5562
|
0.5408
|
0.4800
|
0.4569
|
|
5/8-8 Acme
|
0.625
|
8
|
3G
|
0.6250
|
0.6188
|
0.5578
|
0.5506
|
0.4800
|
0.4692
|
|
5/8-8 Acme
|
0.625
|
8
|
4G
|
0.6250
|
0.6188
|
0.5593
|
0.5542
|
0.4800
|
0.4723
|
|
5/8-8 Acme
|
0.625
|
8
|
5G
|
0.6250
|
0.6188
|
0.5625
|
0.5584
|
0.4800
|
0.4738
|
|
3/4-6 Acme
|
0.75
|
6
|
2G
|
0.7500
|
0.7417
|
0.6598
|
0.6424
|
0.5633
|
0.5372
|
|
3/4-6 Acme
|
0.75
|
6
|
3G
|
0.7500
|
0.7417
|
0.6615
|
0.6534
|
0.5633
|
0.5511
|
|
3/4-6 Acme
|
0.75
|
6
|
4G
|
0.7500
|
0.7417
|
0.6632
|
0.6574
|
0.5633
|
0.5546
|
|
3/4-6 Acme
|
0.75
|
6
|
5G
|
0.7500
|
0.7417
|
0.6667
|
0.662
|
0.5633
|
0.5563
|
|
7/8-6 Acme
|
0.875
|
6
|
2G
|
0.8750
|
0.8667
|
0.7842
|
0.7663
|
0.6883
|
0.6615
|
|
7/8-6 Acme
|
0.875
|
6
|
3G
|
0.8750
|
0.8667
|
0.7861
|
0.7778
|
0.6883
|
0.6758
|
|
7/8-6 Acme
|
0.875
|
6
|
4G
|
0.8750
|
0.8667
|
0.788
|
0.782
|
0.6883
|
0.6794
|
|
7/8-6 Acme
|
0.875
|
6
|
5G
|
0.8750
|
0.8667
|
0.7917
|
0.7869
|
0.6883
|
0.6811
|
|
1-5 Acme
|
1
|
5
|
2G
|
1.0000
|
0.9900
|
0.892
|
0.8726
|
0.7800
|
0.7509
|
|
1-5 Acme
|
1
|
5
|
3G
|
1.0000
|
0.9900
|
0.894
|
0.8849
|
0.7800
|
0.7664
|
|
1-5 Acme
|
1
|
5
|
4G
|
1.0000
|
0.9900
|
0.896
|
0.8895
|
0.7800
|
0.7703
|
|
1-5 Acme
|
1
|
5
|
5G
|
1.0000
|
0.9900
|
0.9
|
0.8948
|
0.7800
|
0.7722
|
|
1 1/8-5 Acme
|
1.125
|
5
|
2G
|
1.1250
|
1.1150
|
1.0165
|
0.9967
|
0.9050
|
0.8753
|
|
1 1/8-5 Acme
|
1.125
|
5
|
3G
|
1.1250
|
1.1150
|
1.0186
|
1.0094
|
0.9050
|
0.8912
|
|
1 1/8-5 Acme
|
1.125
|
5
|
4G
|
1.1250
|
1.1150
|
1.0208
|
1.0142
|
0.9050
|
0.8951
|
|
1 1/8-5 Acme
|
1.125
|
5
|
5G
|
1.1250
|
1.1150
|
1.025
|
1.0197
|
0.9050
|
0.8971
|
|
1 1/4-5 Acme
|
1.25
|
5
|
2G
|
1.2500
|
1.2400
|
1.1411
|
1.121
|
1.0300
|
0.9998
|
|
1 1/4-5 Acme
|
1.25
|
5
|
3G
|
1.2500
|
1.2400
|
1.1433
|
1.1339
|
1.0300
|
1.0159
|
|
1 1/4-5 Acme
|
1.25
|
5
|
4G
|
1.2500
|
1.2400
|
1.1455
|
1.1388
|
1.0300
|
1.0199
|
|
1 1/4-5 Acme
|
1.25
|
4
|
5G
|
1.2500
|
1.2400
|
1.15
|
1.1446
|
1.0300
|
1.0219
|
|
1 3/8-4 Acme
|
1.375
|
4
|
2G
|
1.3750
|
1.3625
|
1.2406
|
1.2188
|
1.1050
|
1.0720
|
|
1 3/8-4 Acme
|
1.375
|
4
|
3G
|
1.3750
|
1.3625
|
1.243
|
1.2327
|
1.1050
|
1.0896
|
|
1 3/8-4 Acme
|
1.375
|
4
|
4G
|
1.3750
|
1.3625
|
1.2453
|
1.238
|
1.1050
|
1.0940
|
|
1 3/8-4 Acme
|
1.375
|
4
|
5G
|
1.3750
|
1.3625
|
1.25
|
1.2441
|
1.1050
|
1.0962
|
|
1 1/2-4 Acme
|
1.5
|
4
|
2G
|
1.5000
|
1.4875
|
1.3652
|
1.3429
|
1.2300
|
1.1965
|
|
1 1/2-4 Acme
|
1.5
|
4
|
3G
|
1.5000
|
1.4875
|
1.3677
|
1.3573
|
1.2300
|
1.2144
|
|
1 1/2-4 Acme
|
1.5
|
4
|
4G
|
1.5000
|
1.4875
|
1.3701
|
1.3627
|
1.2300
|
1.2189
|
|
1 1/2-4 Acme
|
1.5
|
4
|
5G
|
1.5000
|
1.4875
|
1.375
|
1.369
|
1.2300
|
1.2210
|
|
1 3/4-4 Acme
|
1.75
|
4
|
2G
|
1.7500
|
1.7375
|
1.6145
|
1.5916
|
1.4800
|
1.4456
|
|
1 3/4-4 Acme
|
1.75
|
4
|
3G
|
1.7500
|
1.7375
|
1.6171
|
1.6064
|
1.4800
|
1.4640
|
|
1 3/4-4 Acme
|
1.75
|
4
|
4G
|
1.7500
|
1.7375
|
1.6198
|
1.6122
|
1.4800
|
1.4686
|
|
1 3/4-4 Acme
|
1.75
|
4
|
5G
|
1.7500
|
1.7375
|
1.625
|
1.6189
|
1.4800
|
1.4708
|
|
2-4 Acme
|
2
|
4
|
2G
|
2.0000
|
1.9875
|
1.8637
|
1.8402
|
1.7300
|
1.6948
|
|
2-4 Acme
|
2
|
4
|
3G
|
2.0000
|
1.9875
|
1.8665
|
1.8555
|
1.7300
|
1.7135
|
|
2-4 Acme
|
2
|
4
|
4G
|
2.0000
|
1.9875
|
1.8693
|
1.8615
|
1.7300
|
1.7183
|
|
2-4 Acme
|
2
|
4
|
5G
|
2.0000
|
1.9875
|
1.875
|
1.8687
|
1.7300
|
1.7206
|
|
2 1/4-3 Acme
|
2.25
|
3
|
2G
|
2.2500
|
2.2333
|
2.0713
|
2.045
|
1.8967
|
1.8572
|
|
2 1/4-3 Acme
|
2.25
|
3
|
3G
|
2.2500
|
2.2333
|
2.0743
|
2.062
|
1.8967
|
1.8783
|
|
2 1/4-3 Acme
|
2.25
|
3
|
4G
|
2.2500
|
2.2333
|
2.0773
|
2.0685
|
1.8967
|
1.8835
|
|
2 1/4-3 Acme
|
2.25
|
3
|
5G
|
2.2500
|
2.2333
|
2.0833
|
2.0763
|
1.8967
|
1.8862
|
|
2 1/2-3 Acme
|
2.5
|
3
|
2G
|
2.5000
|
2.4833
|
2.3207
|
2.2939
|
2.1467
|
2.1065
|
|
2 1/2-3 Acme
|
2.5
|
3
|
3G
|
2.5000
|
2.4833
|
2.3238
|
2.3113
|
2.1467
|
2.1279
|
|
2 1/2-3 Acme
|
2.5
|
3
|
4G
|
2.5000
|
2.4833
|
2.327
|
2.3181
|
2.1467
|
2.1333
|
|
2 1/2-3 Acme
|
2.5
|
3
|
5G
|
2.5000
|
2.4833
|
2.333
|
2.3262
|
2.1467
|
2.1360
|
|
2 3/4-3 Acme
|
2.75
|
3
|
2G
|
2.7500
|
2.7333
|
2.57
|
2.5427
|
2.3967
|
2.3558
|
|
2 3/4-3 Acme
|
2.75
|
3
|
3G
|
2.7500
|
2.7333
|
2.5734
|
2.567
|
2.3967
|
2.3776
|
|
2 3/4-3 Acme
|
2.75
|
3
|
4G
|
2.7500
|
2.7333
|
2.5767
|
2.5676
|
2.3967
|
2.3831
|
|
2 3/4-3 Acme
|
2.75
|
3
|
5G
|
2.7500
|
2.7333
|
2.5833
|
2.576
|
2.3967
|
2.3858
|
|
3-2 Acme
|
3
|
2
|
2G
|
3.0000
|
2.9750
|
2.736
|
2.7044
|
2.4800
|
2.4326
|
|
3-2 Acme
|
3
|
2
|
3G
|
3.0000
|
2.9750
|
2.7395
|
2.7248
|
2.4800
|
2.4579
|
|
3-2 Acme
|
3
|
2
|
4G
|
3.0000
|
2.9750
|
2.743
|
2.7325
|
2.4800
|
2.4642
|
|
3-2 Acme
|
3
|
2
|
5G
|
3.0000
|
2.9750
|
2.75
|
2.7416
|
2.4800
|
2.4674
|
|
3 1/2-2 Acme
|
3.5
|
2
|
2G
|
3.5000
|
3.4750
|
3.235
|
3.2026
|
2.9800
|
2.9314
|
|
3 1/2-2 Acme
|
3.5
|
2
|
3G
|
3.5000
|
3.4750
|
3.2388
|
3.2237
|
2.9800
|
2.9574
|
|
3 1/2-2 Acme
|
3.5
|
2
|
4G
|
3.5000
|
3.4750
|
3.2425
|
3.2317
|
2.9800
|
2.9638
|
|
3 1/2-2 Acme
|
3.5
|
2
|
5G
|
3.5000
|
3.4750
|
3.25
|
3.2413
|
2.9800
|
2.9669
|
|
4-2 Acme
|
4
|
2
|
2G
|
4.0000
|
3.9750
|
3.734
|
3.7008
|
3.4800
|
3.4302
|
|
4-2 Acme
|
4
|
2
|
3G
|
4.0000
|
3.9750
|
3.738
|
3.7225
|
3.4800
|
3.4568
|
|
4-2 Acme
|
4
|
2
|
4G
|
4.0000
|
3.9750
|
3.742
|
3.7309
|
3.4800
|
3.4634
|
|
4-2 Acme
|
4
|
2
|
5G
|
4.0000
|
3.9750
|
3.75
|
3.7411
|
3.4800
|
3.4666
|
|
4 1/2-2 Acme
|
4.5
|
2
|
2G
|
4.5000
|
4.4750
|
4.233
|
4.1991
|
3.9800
|
3.9291
|
|
4 1/2-2 Acme
|
4.5
|
2
|
3G
|
4.5000
|
4.4750
|
4.2373
|
4.2215
|
3.9800
|
3.9563
|
|
4 1/2-2 Acme
|
4.5
|
2
|
4G
|
4.5000
|
4.4750
|
4.2415
|
4.2302
|
3.9800
|
3.9631
|
|
4 1/2-2 Acme
|
4.5
|
2
|
5G
|
4.5000
|
4.4750
|
4.25
|
4.2409
|
3.9800
|
3.9663
|
|
5-2 Acme
|
5
|
2
|
2G
|
5.0000
|
4.9750
|
4.7319
|
4.6973
|
4.4800
|
4.4281
|
|
5-2 Acme
|
5
|
2
|
3G
|
5.0000
|
4.9750
|
4.7364
|
4.7202
|
4.4800
|
4.4557
|
|
5-2 Acme
|
5
|
2
|
4G
|
5.0000
|
4.9750
|
4.7409
|
4.7294
|
4.4800
|
4.4627
|
|
5-2 Acme
|
5
|
2
|
5G
|
5.0000
|
4.9750
|
4.75
|
4.7408
|
4.4800
|
4.4662
|
