Carriage Bolt Sizes Chart | Threads per Inch
What’s a Carriage Bolt?
Like all bolts, carriage bolts are externally threaded fasteners that are secured with a nut. They’re primarily meant to secure metal to wood, however, some woodworkers leverage them for fastening two pieces of wood together. What differentiates carriage bolts from other types is that the head is characterized by a truss (mushroom) shape. Additionally, the section beneath the head takes the form of a square before transitioning into a rounded shank. This enables the bolt to lock into a square hole bracket, which means it can be fastened with a single wrench. At the same time, the combination of these two features results in the bolt only being accessible from one side. Consequently, carriage bolts have become more popular for security applications where the user can only remove the fastener from the inside.
Carriage Bolt Sizes
| Bolt Diameter | Coarse Thread |
| 1/4″ | 20 |
| 5/16″ | 18 |
| 3/8″ | 16 |
| 7/16″ | 14 |
| 1/2″ | 13 |
| 9/16″ | 12 |
| 5/8″ | 11 |
| 3/4″ | 10 |
| 7/8″ | 9 |
| 1″ | 8 |
Carriage Bolt Types
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