Bolt Head Dimensions
The strength of a bolt is determined by its diameter and the strength of the material from which it is made. Minimum material strengths for various grades of bolts are given in a related page. Here, we deal with the diameter.
It may seem that the determination of a bolt's diameter is a simple matter of measurement, and this is indeed the case when the shank is exposed. In many cases, however, the shank is hidden, and the engineer who is charged with determining the strength of the bolted joint must infer the bolt's diameter from the size of its head. Fortunately, there are standards that govern the relationship between bolt size and head size. The following tables are based on information in the following:
- ANSI B 18.2.1 (Square, Hex, and Heavy Hex)
- ASTM A325 and A490 (High Strength Structural)
- AISC Manual of Steel Contruction (all)
Square Heads
| Square Bolt Dimensions (inches) |
| D |
F |
C |
H |
| 1/4 |
3/8 |
1/2 |
3/16 |
| 3/8 |
9/16 |
13/16 |
1/4 |
| 1/2 |
3/4 |
1 1/16 |
5/16 |
| 5/8 |
15/16 |
1 5/16 |
7/16 |
| 3/4 |
1 1/8 |
1 9/16 |
1/2 |
| 7/8 |
1 5/16 |
1 7/8 |
5/8 |
|
| 1 |
1 1/2 |
2 1/8 |
11/16 |
| 1 1/8 |
1 11/16 |
2 3/8 |
3/4 |
| 1 1/4 |
1 7/8 |
2 5/8 |
7/8 |
| 1 3/8 |
2 1/16 |
2 15/16 |
15/16 |
| 1 1/2 |
2 1/4 |
3 3/16 |
1 |
Hex Heads
| Hex Bolt Dimensions (inches) |
| D |
F |
C |
H |
| 1/4 |
7/16 |
1/2 |
3/16 |
| 3/8 |
9/16 |
5/8 |
1/4 |
| 1/2 |
3/4 |
7/8 |
3/8 |
| 5/8 |
15/16 |
1 1/16 |
7/16 |
| 3/4 |
1 1/8 |
1 5/16 |
1/2 |
| 7/8 |
1 5/16 |
1 1/2 |
9/16 |
|
| 1 |
1 1/2 |
1 3/4 |
11/16 |
| 1 1/8 |
1 11/16 |
1 15/16 |
3/4 |
| 1 1/4 |
1 7/8 |
2 3/16 |
7/8 |
| 1 3/8 |
2 1/16 |
2 3/8 |
15/16 |
| 1 1/2 |
2 1/4 |
2 5/8 |
1 |
| 1 3/4 |
2 5/8 |
3 |
1 3/16 |
|
| 2 |
3 |
3 7/16 |
1 3/8 |
| 2 1/4 |
3 3/8 |
3 7/8 |
1 1/2 |
| 2 1/2 |
3 3/4 |
4 5/16 |
1 11/16 |
| 2 3/4 |
4 1/8 |
4 3/4 |
1 13/16 |
|
| 3 |
4 1/2 |
5 3/16 |
2 |
| 3 1/4 |
4 7/8 |
5 5/8 |
2 3/16 |
| 3 1/2 |
4 7/8 |
5 5/8 |
2 3/16 |
| 3 3/4 |
5 5/8 |
5 1/2 |
2 1/2 |
|
| 4 |
6 |
6 15/16 |
2 11/16 |
Heavy Hex Heads
| Heavy Hex Bolt Dimensions (inches) |
| D |
F |
C |
H |
| 1/2 |
7/8 |
1 |
3/8 |
| 5/8 |
1 1/16 |
1 1/4 |
7/16 |
| 3/4 |
1 1/4 |
1 7/16 |
1/2 |
| 7/8 |
1 7/16 |
1 11/16 |
9/16 |
|
| 1 |
1 5/8 |
1 7/8 |
11/16 |
| 1 1/8 |
1 13/16 |
2 1/16 |
3/4 |
| 1 1/4 |
2 |
2 5/16 |
7/8 |
| 1 3/8 |
2 3/16 |
2 1/2 |
15/16 |
| 1 1/2 |
2 3/8 |
2 3/4 |
1 |
| 1 3/4 |
2 3/4 |
3 3/16 |
1 3/16 |
|
| 2 |
3 1/8 |
3 5/8 |
1 3/8 |
| 2 1/4 |
3 1/2 |
4 1/16 |
1 1/2 |
| 2 1/2 |
3 7/8 |
4 1/2 |
1 11/16 |
| 2 3/4 |
4 1/4 |
4 15/16 |
1 13/16 |
|
| 3 |
4 5/8 |
5 5/16 |
2 |
High Strength Structural Bolt Heads
| High Strength Structural Bolt Dimensions (inches) |
| D |
F |
H |
| 1/2 |
7/8 |
5/16 |
| 5/8 |
1 1/16 |
25/64 |
| 3/4 |
1 1/4 |
15/32 |
| 7/8 |
1 7/16 |
35/64 |
|
| 1 |
1 5/8 |
39/64 |
