What Is a Carriage Bolt and How to Use It
By Mutual Screw & Supply | Published: 2026-10-22
Category: How-to Guides
A carriage bolt is a fastener with a domed head and square neck that prevents spinning during installation. This guide explains its uses and how to install it correctly.
Quick Answer
A carriage bolt is a fastener with a smooth, rounded head and a square neck that prevents the bolt from turning during installation. It is ideal for wood-to-wood and wood-to-metal connections.
When to Choose a Fully Threaded Carriage Bolt
Fully threaded carriage bolts, like the 1/4-20 X 7/8" Carriage Bolts in A307 Grade A Plain Steel, provide grip along the entire shank. This makes them suitable for applications where the bolt passes completely through the material and a nut is used on the opposite side. The coarse thread is designed for use in wood and with nuts and washers.
Plain Steel vs. Other Finishes
Plain steel carriage bolts offer good strength at a lower cost but lack corrosion resistance. They are best for indoor or dry applications. For outdoor or damp environments, consider galvanized or stainless steel options to prevent rust.
Frequently Asked Questions
- What is a carriage bolt used for?
- Carriage bolts are primarily used for wood-to-wood and wood-to-metal connections. Common applications include attaching hardware to wood, assembling furniture, and building decks or fences.
- How do I install a carriage bolt?
- Drill a pilot hole slightly smaller than the bolt diameter. Insert the bolt through the material, then hammer the head lightly to seat the square neck. Tighten the nut with a wrench while the square neck prevents the bolt from spinning. Always drill a pilot hole to avoid splitting the wood and to ensure the square neck engages properly.
- Can I use a carriage bolt without a nut?
- Yes, when used in wood, the coarse threads can grip directly into the material. However, for maximum holding strength, especially in softwood or when joining thicker pieces, use a washer and nut on the opposite side.
Product Facts
- 1/4-20 X 7/8" Carriage Bolts | Fully Threaded | A307 Grade A Plain Steel (400 / Pkg.): 1/4-20 X 7/8" Carriage Bolts in A307 Grade A Plain Steel feature a smooth, rounded head with a square neck that prevents the bolt from turning during installation. The square neck pulls into the material, allowing you to tighten the nut without needing a tool to hold the bolt head.
1/4-20 X 7/8" Carriage Bolts | Fully Threaded | A307 Grade A Plain Steel (400 / Pkg.)
