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

In this review the reviewer focuses on a heavy duty construction lag screw intended for outdoor structural work; the bottom line is straightforward: this set is for builders and DIYers who need dependable long fasteners that resist corrosion and drive quickly. The most convincing reason to buy is the combination of a Type 17 notched point for quick starts and a proven triple coating that passed a 1200 hour salt spray test, which together mean fewer broken starters and long life in ACQ treated lumber.

Key Features

• Size and fit: The roughly 5/16in thread diameter and 16in length make these screws suitable for joining large dimensional lumber where deep penetration and clamping force are required.
• Type 17 point: The notched extra sharp point reduces walking and often removes the need for pre-drilling, speeding up layout and installation on deck and pergola posts.
• Heat treated strength: Manufactured from high quality heat treated steel, these lag screws offer superior shear and compression performance compared with standard lag bolts.
• Corrosion protection: A triple coating passed the 1200 hour salt spray test without coating failures, which increases longevity in exterior and ACQ treated lumber applications.
• Drive system: Torx/Star drive provides more bit engagement and reduces cam-out during high-torque installation compared with slotted or Phillips heads.
• Washer head: The modified truss washer head improves bearing area and helps pull framing members tighter for stronger joints.

Who It's For

This product is aimed at contractors, deck builders, and serious DIYers who work with large timber like 4x6s or 6x6s and need deep, reliable fasteners for structural connections. The combination of heat treated steel and heavy corrosion coating makes it appropriate for outdoor projects and for use with ACQ treated lumber.

Those who should look elsewhere include people needing short screws for trim work or applications where a finished countersunk head is required; this is a structural lag intended for pull-down strength rather than finish carpentry.

Pros & Cons

Pros

• High strength from heat treated steel provides superior shear and compression performance for structural joints.
• Type 17 notched point and Torx drive reduce walking and make starts faster with less pre-drilling needed.
• Triple coating that passed extended salt spray testing offers excellent corrosion resistance for exterior use.
• Modified truss washer head increases bearing area and helps pull lumber tight for secure connections.

Cons

• Length and heavy duty design make these unsuitable for trim or finish work where a smaller or countersunk screw is required.
• Specialized fastener may require the correct Torx bit and proper installation torque for best performance.

Specifications

Thread diameter	~5/16in
Length	16in
Head diameter	11/16in
Point type	Type 17 notched extra sharp point
Drive type	Torx/Star drive
Material and finish	Heat treated steel, triple coated
Corrosion test	Passed 1200 hour salt spray without coating failures

Our Verdict

The construction lag screw is a solid choice for anyone building decks, pergolas, or heavy timber frames where long reach, strong shear capacity, and corrosion resistance matter. It offers clear value for exterior structural work thanks to the Type 17 point that reduces pre-drilling and the robust coating that stands up to treated lumber and marine-adjacent conditions.

Frequently Asked Questions

Do these screws work with ACQ treated lumber?
Yes. The triple coating and material choice make them compatible with ACQ treated lumber to resist corrosion.

Will I need to pre-drill pilot holes?
The Type 17 notched point reduces the need for pre-drilling in many situations, though very dense hardwoods or precise alignment may still benefit from pilot holes.

What driver bit should I use?
Use a Torx/Star driver bit sized to the head to minimize cam-out and to apply proper torque during installation.