5/16 in x 5 in Carriage Bolt Kit (50 Pack) - Hot Dip Galvanized

Our review of this 5/16 in x 5 in carriage bolt kit finds it best suited for builders and serious DIYers who need long-lasting exterior fasteners. The bottom line: this 50 pack delivers consistent sizes and a durable hot dip galvanized finish that stands up to exterior environments, making it a straightforward choice for decks, pergolas and other heavy duty timber connections where a semi-flush head is preferred.

Key Features

• 5/16 in diameter, 5 in length: Provides deep embedment for thick timbers and multi-layer structural connections without relying on extension pieces.
• Hot dip galvanized coating: Offers superior corrosion resistance for exterior use and compatibility with ACQ treated lumber.
• Complete 50-piece kit: Includes 50 Grade 307A carriage bolts, 50 USS thick washers and 50 Grade 2/A hex nuts so projects can proceed without parts hunting.
• Semi-flush flat head: The flat head gives a neat, semi-flush finish that reduces snags and looks tidy on decks and gazebos.
• Standards compliant: Meets or exceeds common mechanical and hardware standards, ensuring consistent fit and performance in structural uses.

Who It's For

This kit is aimed at contractors, carpenters and experienced DIY enthusiasts working on outdoor projects such as decks, pergolas, gazebos and heavy timber framing where long carriage bolts are required. The included USS washers and Grade 2/A nuts make it convenient for teams that need uniform hardware in bulk.

Those doing light indoor tasks or requiring specialty head types should look elsewhere; the carriage bolt head is designed for a semi-flush finish and is not ideal where a countersunk or decorative exposed head is desired.

Pros & Cons

Pros

• Durable hot dip galvanized finish that resists corrosion on exterior projects.
• Complete kit packaging with 50 bolts, washers and nuts saves trip time and ensures matching parts.
• Long 5 in length and sturdy 5/16 in diameter work well for thick timbers and multi-piece assemblies.
• Meets recognized industry standards, giving confidence in dimensional and mechanical consistency.

Cons

• Grade 2/A nuts are adequate for structural assembly but not intended for high-strength critical connections where higher grade hardware might be required.
• The flat head is semi-flush but may not suit projects that need a fully flush countersunk appearance.

Specifications

Diameter	5/16 in
Length	5 in
Head diameter	0.703 in
Washer outside diameter	7/8 in
Nut size	5/16-18, wrench 1/2 in
Kit quantity	50 bolts, 50 USS washers, 50 hex nuts
Coating	Hot dip galvanized for exterior use

Our Verdict

This 5/16 in x 5 in carriage bolt kit is a practical, cost-effective choice for outdoor timber work where corrosion resistance and consistent hardware are important. Buy it if you need long bolts with a semi-flush finish and a complete parts kit; those needing higher strength grades or decorative heads should consider other options.

Frequently Asked Questions

Are these bolts suitable for ACQ treated lumber?
Yes. The hot dip galvanized coating is specified as suitable for use with ACQ treated lumber to resist corrosion.

What is included in the kit?
The kit contains 50 Grade 307A carriage bolts, 50 USS thick washers and 50 Grade 2/A hex nuts, all hot dip galvanized.

What wrench size fits the nuts?
The hex nuts use a 1/2 in wrench size for tightening.