Grade 5 vs A307 Carriage Bolts: Strength Comparison
By Mutual Screw & Supply | Published: 2026-10-25
Category: Comparisons
Compare Grade 5 hex head cap screws and A307 Grade A carriage bolts for strength, finish, and application. Learn which fastener suits your project.
Quick answer
Grade 5 hex head cap screws offer higher tensile strength and are better for machinery and equipment assembly, while A307 Grade A carriage bolts provide sufficient strength for wood-to-wood and wood-to-metal connections with anti-rotation security.
Strength and material differences
Grade 5 steel is a medium-carbon steel that has been heat-treated to achieve higher tensile strength than standard Grade 2 or A307 fasteners. This makes it suitable for applications where the bolt bears significant load, such as in machinery or equipment assembly.
A307 Grade A is a low-carbon steel bolt with lower tensile strength. It is designed for general-purpose fastening where high strength is not the primary concern. Its strength is adequate for most wood and light metal connections.
The trade-off is clear: Grade 5 provides more strength but at a higher cost, while A307 is more economical for less demanding jobs.
Design and installation differences
Hex head cap screws have a hexagonal head designed for wrench or socket drive. They are typically used in tapped holes or with nuts and are common in metal-to-metal fastening.
Carriage bolts have a smooth, domed head and a square neck underneath that pulls into the material to prevent the bolt from turning during installation. This design is ideal for wood-to-wood and wood-to-metal connections where the bolt must not spin.
The trade-off is that hex head cap screws require a wrench or socket and access to both sides, while carriage bolts self-lock in wood but need a nut on the opposite side.
Finish and corrosion resistance
Grade 5 hex head cap screws often come with a yellow zinc (CR+6) finish, which provides moderate corrosion resistance. This finish is common in industrial and automotive applications.
A307 Grade A carriage bolts typically have a zinc plated finish. Zinc plating offers good corrosion protection for indoor and general outdoor use, though it is less durable than some higher-end coatings.
The trade-off is that yellow zinc is slightly more corrosion-resistant than standard zinc plating, but both are suitable for most dry or mildly damp environments.
Trade-offs at a glance
- Strength: Grade 5 hex head cap screws offer higher tensile strength than A307 Grade A carriage bolts. Choose Grade 5 for load-bearing metal assemblies; choose A307 for general wood or light metal fastening.
- Installation: Hex head cap screws require a wrench or socket and access to both sides. Carriage bolts self-lock in wood via the square neck, needing only a nut on the opposite side.
- Corrosion resistance: Yellow zinc finish (Grade 5) provides moderate corrosion resistance. Zinc plating (A307) is suitable for indoor and general outdoor use but may not hold up in harsh environments. For outdoor or wet conditions, consider upgrading to a stainless steel or coated fastener.
- Cost: Grade 5 hex head cap screws are more expensive due to higher strength and heat treatment. A307 carriage bolts are more economical for projects where high strength is not needed.
Product facts
- 9/16-12 X 3-1/2" Hex Head Cap Screws | Grade 5 Steel Yellow Zinc | Partially Threaded (25 / Pkg.): 9/16-12 x 3-1/2" hex head cap screws in Grade 5 steel with yellow zinc finish, partially threaded, sold in packs of 25. The Grade 5 rating means these bolts are heat-treated for higher strength, ideal for machinery and equipment assembly where load-bearing is critical.
9/16-12 X 3-1/2" Hex Head Cap Screws | Grade 5 Steel Yellow Zinc | Partially Threaded (25 / Pkg.) - 1/2-13 X 6-1/2" Carriage Bolts | A307 Grade A Zinc Plated Steel (25 / Pkg.): 1/2-13 x 6-1/2" carriage bolts in A307 Grade A zinc plated steel, with a domed head and square anti-rotation neck, sold in packs of 25. The square neck prevents spinning during installation, making these bolts perfect for wood connections where you need a secure, non-slip fastening.
1/2-13 X 6-1/2" Carriage Bolts | A307 Grade A Zinc Plated Steel (25 / Pkg.)
Which fastener should you choose?
Best for
- Grade 5 hex head cap screws: machinery assembly, equipment mounting, and any application requiring high tensile strength in metal-to-metal fastening.
- A307 Grade A carriage bolts: wood-to-wood connections, wood-to-metal attachments, and general construction where anti-rotation is beneficial.
Not for
- Grade 5 hex head cap screws: wood connections where the bolt needs to resist turning; use carriage bolts instead.
- A307 Grade A carriage bolts: high-stress metal assemblies or applications requiring Grade 5 or higher strength ratings.
