Carriage Bolts Threads per Inch Sizes Diameter vs Coarse

Carriage Bolt Sizes Chart | Threads per Inch

Carriage Bolt Sizes Chart Threads per Inch SAE Dimensions Guide

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

Carriage Bolt Types - Half Threaded Partially

As the name implies, the shank on this type of carriage bolt is only threaded part of the length. This style is typically seen on longer sizes.
Carriage Bolt Types- Fully Threaded

Fully threaded carriage bolts can be used to fasten two narrow objects together, which is why shorter lengths are normally seen in this style.
Carriage Bolt Types - Slotted Head

Slotted carriage bolts are unique in that the head can still be held in place during fastening if there isn’t a square hole to lock bolt into place. This feature doesn’t compromise the bolt’s usage in security applications.
Carriage Bolt Types - Plow Bolts

Plow bolts work and function much the same as any other carriage bolt. The only difference is that the head shape is countersunk rather truss. This means that the bolt can be fastened to sit flush with the surface.
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