Carriage Bolt 5/16-18 x 3 in Galvanized, 100 PCS - Durable Fastening

In this review the Hillman carriage bolts are judged on durability and fit for common carpentry and metalwork tasks; they are best for DIYers and contractors who need a bulk supply of fasteners that resist rust and provide a neat, semi-flush finish. The single biggest reason to buy is the combination of the self-locking square neck and galvanized coating, which together make these bolts easy to set into wood and give reasonable corrosion protection for exterior or indoor projects.

Key Features

• Self-locking square neck: The square underside of the head sits into a predrilled hole to prevent the head from turning during installation, simplifying assembly without a separate driving tool.
• Flat head design: The flat rounded head provides a semi-flush finish that hides the fastener while eliminating the need for a washer in many wood-to-wood and wood-to-metal joints.
• Galvanized finish: Zinc plating reduces the risk of rust in moderate outdoor conditions, extending service life compared with plain steel bolts.
• Bulk pack of 100: Supplied in a 100 piece quantity to cover multiple projects or on-site needs, which is convenient for builders and hobbyists.
• Standard thread size: The 5/16-18 thread is a common pitch that fits into pre tapped or nut-equipped assemblies for secure clamping.

Who It's For

These carriage bolts suit homeowners tackling deck repairs, fence building, pergola assembly and other woodwork where a rounded head and square neck are desirable. Tradespeople who install many wood-to-metal connections will appreciate the time saved by the self-locking head and the economy of a 100 piece pack.

They are less appropriate for applications requiring heavy marine exposure or stainless steel corrosion resistance, or where precision thread quality is critical for tapped metal parts; customers needing fine-thread perfection or highly corrosive environment protection should consider specialty fasteners instead.

Pros & Cons

Pros

• Galvanized coating offers practical rust resistance for most exterior and indoor projects.
• Square neck prevents spinning so installation is faster and easier without extra tools.
• Flat head gives a neat, semi-flush appearance and can eliminate the need for washers.
• Pack of 100 provides good value and reduces repeat ordering for large jobs.

Cons

• Some customers report inconsistent thread quality, so a small number may not thread smoothly in all applications.
• Galvanized finish can appear chalky and is not a substitute for stainless steel in highly corrosive environments.

Specifications

Product type	Carriage bolt
Size	5/16-18 x 3 in
Finish	Galvanized (zinc plated)
Quantity	100 pieces
Head style	Round flat head with square neck
Typical use	Wood-to-wood and wood-to-metal fastening

Our Verdict

For most DIYers and contractors who need a reliable, economical bulk pack of carriage bolts, these deliver good value thanks to the self-locking square neck and galvanized finish. They perform well in standard outdoor and indoor projects, though buyers should inspect threads if using in precision metal tapping or very corrosive environments.

Frequently Asked Questions

Are these bolts suitable for outdoor use?
Yes, the galvanized finish provides moderate corrosion resistance appropriate for typical outdoor and covered exposures.

Do these require a washer?
The flat head design is intended to eliminate the need for a washer in many wood applications, though a washer or nut may still be used on the far side for added clamping.

Will the head spin during installation?
No, the square underside of the head is self-locking when seated in a square or tight hole, which prevents the head from turning.