Carriage Bolts

Carriage bolts, also known as coach bolts or round head square neck bolts, are a type of fastener used to secure two pieces of material together. They are typically used in woodworking and construction applications where a smooth, finished appearance is desired on one side of the joint.

Carriage bolts have several distinctive features:

  • Head: Carriage bolts have a round, domed head with a flat or slightly curved top surface. This design allows them to be countersunk into the material, providing a flush or low-profile finish on the surface.
  • Square Neck: Beneath the head of the carriage bolt, there is a square-shaped section that prevents the bolt from rotating when tightened. This square neck fits into a square hole or slot in the material, preventing the bolt from turning when a nut is being tightened onto it.
  • Threaded Shaft: The shaft of a carriage bolt is threaded along its entire length, which allows it to be inserted through two pieces of material and secured by tightening a nut on the opposite side.

Carriage bolts are commonly used in applications where aesthetics matter because the round head and square neck design prevent them from protruding too much from the surface of the material. They are often used in building outdoor structures like fences, decks, and wooden playsets, as well as in furniture assembly and other woodworking projects.

When using carriage bolts, it's essential to ensure that the square neck fits securely into the square hole or slot to prevent the bolt from turning when you tighten the nut. This square neck design is what distinguishes carriage bolts from other types of bolts.

AFT Fasteners carries a large selection of Metric and Inch carbon or stainless steel carriage bolts in sizes No. 10, 1/2", 1/4", 3/16", 3/4", 3/8", 5/16", 5/8" 7/16", 1-1/2". 

Types of Carriage Bolts

Depending on your application, we supply a wide array of materials and grades, such as hot dipped galvanized carriage bolts commonly used for outdoor furniture because of the thicker protective coating, Grade-5 and Grade-8 carriage bolts for greater load carrying capacity, or 316 stainless steel carriage bolts for greater corrosion resistance.

When installing sheet metal, choose a round head, short neck as the standard size neck may create an obstruction. And, for soft, ductile metals, wood and plastics, the round head, ribbed neck may be your best option.

Carriage Bolt Resources