Hex cap bolt dimensions are trickier than you think. By default, they are not threaded all the way, so you need to be careful in your design to make sure you are not threading beyond the capability of the bolt itself.
Just as with the standard nut and washer, it it important to consider the geometric constraints of the hex cap bolt to ensure proper function and easier assembly / disassembly.
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Hex Bolt Dimensions
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Basic Product Diameter
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Full-Size Body Diameter
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Width Across Flats
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Width Across Corners
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Head Height
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Thread Length
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Thread Length
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||
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Max
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Min
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Max
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Min
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Up to 6in
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Over 6 in
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|||
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1/4
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.26
|
.237
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7/16
|
.505
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0.484
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11/64
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0.75
|
1.00
|
|
5/16
|
.324
|
.298
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1/2
|
.577
|
0.552
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7/32
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0.88
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1.13
|
|
3/8
|
.388
|
.360
|
9/16
|
.650
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0.62
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1/4
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1.00
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1.25
|
|
7/16
|
.452
|
.421
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5/8
|
.722
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0.687
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19/64
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1.13
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1.38
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|
1/2
|
.515
|
.482
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3/4
|
.866
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0.826
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11/32
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1.25
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1.50
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|
5/8
|
.642
|
.605
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15/16
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1.083
|
1.033
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27/64
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1.50
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1.75
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|
3/4
|
.768
|
.729
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1-1/8
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1.299
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1.24
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1/2
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1.75
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2.00
|
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7/8
|
.895
|
.852
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1-5/16
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1.516
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1.447
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37/64
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2.00
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2.25
|
|
1
|
1.022
|
.976
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1-1/2
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1.732
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1.653
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43/64
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2.25
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2.50
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|
1-1/8
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1.149
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1.098
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1-11/16
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1.949
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1.859
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3/4
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2.50
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2.75
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|
1-1/4
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1.277
|
1.223
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1-7/8
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2.165
|
2.066
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27/32
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2.75
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3.00
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1-3/8
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1.404
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1.345
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2-1/16
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2.382
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2.273
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29/32
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3.00
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3.25
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|
1-1/2
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1.531
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1.47
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2-1/4
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2.598
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2.48
|
1
|
3.25
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3.50
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|
1-3/4
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1.785
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1.716
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2-5/8
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3.031
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2.893
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1-5/32
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3.75
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4.00
|
|
2
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2.039
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1.964
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3
|
3.464
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3.306
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1-11/32
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4.25
|
4.50
|
|
2-1/4
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2.305
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2.214
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3-3/8
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3.897
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3.719
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1-1/2
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4.75
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5.00
|
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2-1/2
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2.559
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2.461
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3-3/4
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4.33
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4.133
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1-21/32
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5.25
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5.5
|
|
2-3/4
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2.827
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2.711
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4-1/8
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4.763
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4.546
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1-13/16
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5.75
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6.00
|
|
3
|
3.081
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2.961
|
4-1/2
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5.196
|
4.959
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2
|
6.25
|
6.50
|
|
3-1/4
|
3.335
|
3.21
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4-7/8
|
5.629
|
5.372
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2-3/16
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6.75
|
7.00
|
|
3-1/2
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3.589
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3.461
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5-1/4
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6.062
|
5.786
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2-5/16
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7.25
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7.50
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|
3-3/4
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3.858
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3.726
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5-5/8
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6.495
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6.198
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2-1/2
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7.75
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8.00
|
|
4
|
4.111
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3.975
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6
|
6.928
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6.612
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2-11/16
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8.25
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8.50
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