Construction Lag Screw 5/16in x 12in Type 17 - Heavy Duty Structural

In this review the focus is on a heavy duty construction lag screw designed for demanding structural work. The bottom line is simple: if you need a long, strong screw that grips deeply and resists corrosion on treated lumber, this product delivers. Built from heat treated steel with a triple coating and a Type 17 notched point, the screw is intended for builders, deck installers and DIYers who want a reliable fastener that reduces pre-drilling and holds 4x6 and similar members tightly.

Key Features

• Type 17 Notched Point: the extra sharp, notched point starts quickly and reduces "walking," making it easier to drive into wood without extensive pilot drilling.
• Heat Treated Steel: manufactured from high quality heat treated steel for improved shear and compression strength compared with standard lag bolts.
• Triple Coating: triple coated finish provides corrosion resistance suitable for ACQ treated lumber and prolonged outdoor use.
• 1200 Hour Salt Spray Performance: the coating passed extended salt spray testing without failures, indicating long-term durability in corrosive environments.
• Large Head and Deep Threads: the roughly 11/16in head and ~5/16in thread diameter pull lumber tight and provide strong bearing surface for structural connections.
• 100 Count Pack: supplied in a bulk quantity that suits larger projects like decks and structural framing where many fasteners are required.

Who It's For

This screw is aimed at professional carpenters, deck builders and serious DIYers who work with heavy lumber and ACQ treated wood and need a reliable structural fastener. Its combination of heat treated steel, robust thread diameter and long 12in length makes it a good choice when connecting wide posts, beams and when deep embedment is required.

Those doing fine woodworking, light trim or projects where a smaller or countersunk fastener is needed should look elsewhere; this product is intended for structural connections and can be overkill for delicate or visible finish work.

Pros & Cons

Pros

• Excellent strength and holding power for structural joins, outperforming common lag bolts in shear and compression.
• Corrosion resistant triple coating and verified 1200 hour salt spray performance for use with ACQ treated lumber.
• Type 17 notched point reduces need for pre-drilling and improves driving speed without walking.

Cons

• Large 12in length and head make these unsuitable for finish carpentry or applications needing concealed fasteners.

Specifications

Thread Diameter	~5/16in
Head Diameter	11/16in
Length	12in
Material	Heat treated steel
Drive Type	Torx/Star drive
Coating	Triple coated, ACQ compatible
Pack Count	100 screws

Our Verdict

For anyone building decks, pergolas or structural frames who needs deep, reliable holding power in treated lumber, this 12in Type 17 construction lag screw is a practical choice. It pairs robust steel construction with a proven coating and a point designed to start quickly, offering strong value for large projects where corrosion resistance and strength matter most.

Frequently Asked Questions

Are these screws suitable for ACQ treated lumber?
Yes. The triple coating and ACQ compatibility are specified so they can be used with treated wood.

Do they require pre-drilling?
The Type 17 notched point reduces the need for pre-drilling in many cases, though pilot holes may still be advisable in very dense hardwoods.

What drive type is required?
They use a Torx/Star drive which offers better torque transfer than common hex heads for heavy driving.