ASME B18.31.2 is the American National Standard for Continuous Thread, Double-End, and Tap End Studs (Inch Series). This standard provides comprehensive dimensional and general data for three primary stud configurations: continuous thread studs (threaded over their complete length), double-end studs (available in clamping and tap-end types), and flange bolting studs. It covers critical specifications for body diameters (reduced and full body), thread lengths, and materials, serving as the essential reference for fasteners used in diverse mechanical and flange-bolting applications.
Dimensions & Size Chart
Continuous Thread Stud Dimensions
Thread Size
1/4
5/16
3/8
7/16
1/2
9/16
5/8
3/4
7/8
1
1-1/8
1-1/4
1-3/8
1-1/2
1-5/8
1-3/4
1-7/8
2
2-1/4
2-1/2
2-3/4
3
Thread Diameter
Nom
0.25
0.3125
0.375
0.4375
0.5
0.5625
0.625
0.75
0.875
1
1.125
1.25
1.375
1.5
1.625
1.75
1.875
2
2.25
2.5
2.75
3
Threads Per Inch
UNC
20
18
16
14
13
12
11
10
9
8
7
7
6
6
—
5
—
4.5
4.5
4
4
4
UNF
28
24
24
20
20
18
18
16
14
12
12
12
12
12
—
—
—
—
—
—
—
—
8UN
—
—
—
—
—
—
—
—
—
—
8
8
8
8
8
8
8
8
8
8
8
8
U
UNC (Min)
0.05
0.056
0.063
0.072
0.077
0.084
0.091
0.1
0.111
0.125
0.143
0.143
0.167
0.167
—
0.2
—
0.222
0.222
0.25
0.25
0.25
UNC (Max)
0.1
0.111
0.125
0.143
0.154
0.167
0.182
0.2
0.222
0.25
0.286
0.286
0.333
0.333
—
0.4
—
0.444
0.444
0.5
0.5
0.5
UNF (Min)
0.036
0.042
0.042
0.05
0.05
0.056
0.056
0.063
0.072
0.084
0.084
0.084
0.084
0.084
—
—
—
—
—
—
—
—
UNF (Max)
0.071
0.083
0.083
0.1
0.1
0.111
0.111
0.125
0.143
0.167
0.167
0.167
0.167
0.167
—
—
—
—
—
—
—
—
8UN (Min)
—
—
—
—
—
—
—
—
—
—
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
8UN (Max)
—
—
—
—
—
—
—
—
—
—
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
Note: All measurements are in inches
Disclaimer: The dimensions presented on this page are based on the applicable industry standard. However, actual product measurements may vary slightly due to manufacturing practices, material selection, surface finish, and specified tolerance classes. Buyers and sourcing professionals are encouraged to verify final specifications with the manufacturer or supplier prior to procurement, particularly for critical applications.
Legend
D – Nominal Diameter: Represents the nominal major diameter of the thread. In practical applications, the actual major diameter will typically be smaller than its nominal value.
Threads Per Inch (TPI): Specifies the total number of threads contained within a one-inch span of the stud.
U – Chamfered Thread Distance: The length of the chamfered thread distance at each end of the stud, designed to facilitate easier engagement with a nut.
LT – Total Length: The overall length of the continuous thread stud, measured from end to end including the points.
Clamping Stud Dimensions
Thread Size
1/4
5/16
3/8
7/16
1/2
9/16
5/8
3/4
7/8
1
1-1/8
1-1/4
1-3/8
1-1/2
1-5/8
1-3/4
1-7/8
2
2-1/4
2-1/2
2-3/4
3
3-1/4
3-1/2
3-3/4
4
(D) Full Body
UNC (Min)
0.241
0.303
0.364
0.426
0.488
0.55
0.611
0.735
0.859
0.983
1.106
1.231
1.354
1.479
—
1.727
—
1.975
2.225
2.473
2.723
2.973
3.223
3.473
3.723
3.973
UNC (Max)
0.25
0.3125
0.375
0.4375
0.5
0.5625
0.625
0.75
0.875
1
1.125
1.25
1.375
1.5
1.625
1.75
1.875
2
2.25
2.5
2.75
3
3.25
3.5
3.75
4
UNF (Min)
0.243
0.304
0.367
0.428
0.491
0.552
0.615
0.739
0.863
0.987
1.112
1.237
1.362
1.487
—
—
—
—
—
—
—
—
—
—
—
—
UNF (Max)
0.25
0.3125
0.375
0.4375
0.5
0.5625
0.625
0.75
0.875
1
1.125
1.25
1.375
1.5
1.625
1.75
1.875
2
2.25
2.5
2.75
3
3.25
3.5
3.75
4
8UN (Max)
0.25
0.3125
0.375
0.4375
0.5
0.5625
0.625
0.75
0.875
1
1.125
1.25
1.375
1.5
1.625
1.75
1.875
2
2.25
2.5
2.75
3
3.25
3.5
3.75
4
8UN (Min)
—
—
—
—
—
—
—
—
—
—
1.108
1.233
1.358
1.483
1.608
1.733
1.858
1.983
2.233
2.483
2.733
2.982
3.223
3.473
3.723
3.973
(D) Reduced Body
UNC (Min)
0.213
0.271
0.329
0.385
0.444
0.502
0.559
0.677
0.795
0.91
1.023
1.148
1.256
1.483
1.608
1.733
1.858
1.983
2.233
2.483
2.733
2.982
3.232
3.482
3.732
3.982
UNC (Max)
0.241
0.303
0.364
0.426
0.488
0.55
0.611
0.735
0.859
0.983
1.106
1.231
1.354
1.479
—
1.727
—
1.975
2.225
2.473
2.723
2.973
3.223
3.473
3.723
3.973
UNF (Min)
0.223
0.281
0.343
0.4
0.462
0.521
0.583
0.703
0.822
0.938
1.063
1.188
1.313
1.438
—
—
—
—
—
—
—
—
—
—
—
—
UNF (Max)
0.243
0.304
0.367
0.428
0.491
0.552
0.615
0.739
0.863
0.987
1.112
1.237
1.362
1.487
—
—
—
—
—
—
—
—
—
—
—
—
8UN (Min)
—
—
—
—
—
—
—
—
—
—
1.035
1.16
1.284
1.409
1.534
1.659
1.784
1.909
2.158
2.408
2.658
2.908
3.158
3.407
3.657
3.907
8UN (Max)
—
—
—
—
—
—
—
—
—
—
1.108
1.233
1.358
1.483
1.608
1.733
1.858
1.983
2.233
2.483
2.733
2.982
3.232
3.482
3.732
3.982
(B) Thread Length
Min L ≤ 10"
0.75
0.875
1
1.125
1.25
1.375
1.5
1.75
2
2.25
2.5
2.75
3
3.25
3.5
3.75
4
4.25
4.75
5.25
5.75
—
—
—
—
—
Min L ≤ 16"
1
1.125
1.25
1.375
1.5
1.625
1.75
2
2.25
2.5
2.75
3
3.25
3.5
3.75
4
4.25
4.5
5
5.5
6
6.5
7
7.5
8
8.5
Min L > 16"
1.5
1.625
1.75
1.875
2
2.125
2.25
2.5
2.75
3
3.25
3.5
3.75
4
4.25
4.5
4.75
5
5.5
6
6.5
7
7.5
8
8.5
9
U
Max UNC
0.1
0.111
0.125
0.143
0.154
0.167
0.182
0.2
0.222
0.25
0.286
0.286
0.333
—
0.4
—
0.444
0.444
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
Max UNF
0.071
0.083
0.083
0.1
0.1
0.111
0.111
0.125
0.143
0.167
0.167
0.167
0.167
0.167
—
—
—
—
—
—
—
—
—
—
—
—
Max 8UN
—
—
—
—
—
—
—
—
—
—
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
Note: All measurements are in inches
Disclaimer: The dimensions presented on this page are based on the applicable industry standard. However, actual product measurements may vary slightly due to manufacturing practices, material selection, surface finish, and specified tolerance classes. Buyers and sourcing professionals are encouraged to verify final specifications with the manufacturer or supplier prior to procurement, particularly for critical applications.
Legend
D – Thread & Body Diameter: Refers to the nominal major diameter of the threads and the diameter of the unthreaded portion of the stud. This includes specifications for both Full Body and Reduced Body diameters.
B – Nut End Thread Length: The minimum length of the threaded section intended for nut engagement. This value varies depending on whether the total length (L) of the stud is less than 10", less than 16", or greater than 16".
U – Point Length: The chamfered thread distance at each end of the stud. It represents the length from the extreme end to the first full form thread to assist in assembly.
Threads Per Inch (TPI): The number of thread peaks per inch of length, categorized by series such as UNC (Coarse), UNF (Fine), or 8UN.
Tap End Stud Dimensions
Thread Size
1/4
5/16
3/8
7/16
1/2
9/16
5/8
3/4
7/8
1
1-1/8
1-1/4
1-3/8
1-1/2
1-5/8
1-3/4
1-7/8
2
2-1/4
2-1/2
2-3/4
3
3-1/4
3-1/2
3-3/4
4
(DR) Full Body
UNC (Min)
0.241
0.303
0.364
0.426
0.488
0.55
0.611
0.735
0.859
0.983
1.106
1.231
1.354
1.479
—
1.727
—
1.975
2.225
2.473
2.723
2.973
3.223
3.473
3.723
3.973
UNC (Max)
0.25
0.3125
0.375
0.4375
0.5
0.5625
0.625
0.75
0.875
1
1.125
1.25
1.375
1.5
1.625
1.75
1.875
2
2.25
2.5
2.75
3
3.25
3.5
3.75
4
UNF (Min)
0.243
0.304
0.367
0.428
0.491
0.552
0.615
0.739
0.863
0.987
1.112
1.237
1.362
1.487
—
—
—
—
—
—
—
—
—
—
—
—
UNF (Max)
0.25
0.3125
0.375
0.4375
0.5
0.5625
0.625
0.75
0.875
1
1.125
1.25
1.375
1.5
1.625
1.75
1.875
2
2.25
2.5
2.75
3
3.25
3.5
3.75
4
8UN (Max)
0.25
0.3125
0.375
0.4375
0.5
0.5625
0.625
0.75
0.875
1
1.125
1.25
1.375
1.5
1.625
1.75
1.875
2
2.25
2.5
2.75
3
3.25
3.5
3.75
4
8UN (Min)
—
—
—
—
—
—
—
—
—
—
1.108
1.233
1.358
1.483
1.608
1.733
1.858
1.983
2.233
2.483
2.733
2.982
3.223
3.473
3.723
3.973
(DR) Reduced Body
UNC (Min)
0.213
0.271
0.329
0.385
0.444
0.502
0.559
0.677
0.795
0.91
1.023
1.148
1.256
1.483
1.608
1.733
1.858
1.983
2.233
2.483
2.733
2.982
3.232
3.482
3.732
3.982
UNC (Max)
0.241
0.303
0.364
0.426
0.488
0.55
0.611
0.735
0.859
0.983
1.106
1.231
1.354
1.479
—
1.727
—
1.975
2.225
2.473
2.723
2.973
3.223
3.473
3.723
3.973
UNF (Min)
0.223
0.281
0.343
0.4
0.462
0.521
0.583
0.703
0.822
0.938
1.063
1.188
1.313
1.438
—
—
—
—
—
—
—
—
—
—
—
—
UNF (Max)
0.243
0.304
0.367
0.428
0.491
0.552
0.615
0.739
0.863
0.987
1.112
1.237
1.362
1.487
—
—
—
—
—
—
—
—
—
—
—
—
8UN (Min)
—
—
—
—
—
—
—
—
—
—
1.035
1.16
1.284
1.409
1.534
1.659
1.784
1.909
2.158
2.408
2.658
2.908
3.158
3.407
3.657
3.907
8UN (Max)
—
—
—
—
—
—
—
—
—
—
1.108
1.233
1.358
1.483
1.608
1.733
1.858
1.983
2.233
2.483
2.733
2.982
3.232
3.482
3.732
3.982
(BM) Tap End Length
8UN (Nom)
0.375
0.469
0.563
0.656
0.75
0.844
0.938
1.125
1.313
1.5
1.688
1.875
2.063
2.25
2.438
2.625
2.813
3
3.375
3.75
4.125
4.5
4.875
5.25
5.625
6
8UN (Min)
0.35
0.44
0.532
0.62
0.708
0.802
0.892
1.075
1.258
1.438
1.625
1.813
2
2.188
2.375
2.563
2.75
2.925
3.3
3.675
4.05
4.425
4.775
5.15
5.525
5.9
8UN (Max)
0.4
0.498
0.594
0.692
0.792
0.896
0.983
1.175
1.368
1.562
1.75
1.938
2.125
2.313
2.5
2.688
2.875
3.075
3.45
3.825
4.2
4.575
4.975
5.35
5.725
6.1
(B) Nut End Length
Min L ≤ 10"
0.75
0.875
1
1.125
1.25
1.375
1.5
1.75
2
2.25
2.5
2.75
3
3.25
3.5
3.75
4
4.25
4.75
5.25
5.75
—
—
—
—
—
Min L ≤ 16"
1
1.125
1.25
1.375
1.5
1.625
1.75
2
2.25
2.5
2.75
3
3.25
3.5
3.75
4
4.25
4.5
5
5.5
6
6.5
7
7.5
8
8.5
Min L > 16"
1.5
1.625
1.75
1.875
2
2.125
2.25
2.5
2.75
3
3.25
3.5
3.75
4
4.25
4.5
4.75
5
5.5
6
6.5
7
7.5
8
8.5
9
U
Max UNC
0.1
0.111
0.125
0.143
0.154
0.167
0.182
0.2
0.222
0.25
0.286
0.286
0.333
0.333
—
0.4
—
0.444
0.444
0.5
0.5
0.5
0.5
0.5
0.5
0.5
Max UNF
0.071
0.083
0.083
0.1
0.1
0.111
0.111
0.125
0.143
0.167
0.167
0.167
0.167
0.167
—
—
—
—
—
—
—
—
—
—
—
—
Max 8UN
—
—
—
—
—
—
—
—
—
—
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
Note: All measurements are in inches
Disclaimer: The dimensions presented on this page are based on the applicable industry standard. However, actual product measurements may vary slightly due to manufacturing practices, material selection, surface finish, and specified tolerance classes. Buyers and sourcing professionals are encouraged to verify final specifications with the manufacturer or supplier prior to procurement, particularly for critical applications.
Legend
D – Thread Major Diameter: The nominal major diameter of the stud threads.
DR – Body Diameter: The diameter of the unthreaded portion of the stud, which may be specified as Full Body or Reduced Body.
BM – Tap End Length: The length of the threaded section intended to be screwed into a tapped hole. This length includes the point and is measured from the extreme end of the stud.
B – Nut End Length: The minimum length of the threaded section intended for nut engagement. This length varies based on the total length of the stud (L).
U – Point Length: The chamfered thread distance at each end of the stud, measured from the extreme end to the first full form thread.
