5/16-18 x 3 1/2 in Self-Tapping Trailer Deck Screws - Durable Fit

In this review of the 5/16-18 x 3 1/2 in self-tapping trailer deck screws the bottom line is straightforward: these fasteners are built for installers who need reliable thread-cutting performance and a flush finish when securing trailer floorboards or similar heavy-duty panels. The reviewer found the Type F point cut into wood and thin plate steel reliably, while the hardened steel with black phosphate and oil coating held up well against handling and outdoor use. If you need a screw that balances cutting ability, torque acceptance and a countersunk look, this is worth considering.

Key Features

• Type F point: cuts threads into wood and thin metal plate so installers can save time by avoiding pre-tapping in many applications.
• Hardened steel construction: provides strength for repeated use and reduces breakage risk when driving into tough decking or trailer framing.
• Black phosphate and oil coating: adds corrosion resistance and helps the screws slide into material more smoothly during installation.
• Star drive T-40: reduces slippage and cam-out so more torque can be applied safely without stripping the head.
• Flat countersunk head: creates a flush finish for a cleaner deck surface and better board-to-board seating when driven correctly.

Who It's For

Contractors, trailer builders, automotive technicians and experienced DIYers who routinely secure floorboards, trailer decks, or equipment beds will appreciate the thread-cutting capability and hardened construction. The screws are geared toward projects where a flush, durable fastening is required and where installers can use a T-40 star bit to maximize torque.

Those who need stainless corrosion resistance for constant saltwater exposure or a decorative exposed-fastener finish should look elsewhere; this product prioritizes strength and thread-forming ability over bright finish or marine-grade metallurgy.

Pros & Cons

Pros

• Type F thread-forming point reliably cuts threads into wood and thin plate steel for fast installs.
• Star drive T-40 head greatly reduces stripping and allows higher torque transfer.
• Hardened steel with black phosphate and oil finish improves durability and corrosion resistance for outdoor use.

Cons

• Not stainless steel, so it is not ideal for continuous saltwater exposure or highly corrosive environments.
• Requires the correct T-40 driver and attention to recommended hole or plate thickness for best fit.

Specifications

Size	5/16-18 x 3 1/2 in
Point type	Type F self-tapping (thread cutting)
Drive	Star drive (Torx) T-40
Head style	Flat countersunk head
Material & finish	Hardened steel, black phosphate with oil coating
Pack quantity	50 pcs

Our Verdict

These screws are a practical choice for anyone fitting trailer decks or securing wood to thin metal where thread-forming ability and a flush finish matter. Their combination of hardened steel, T-40 drive and Type F point deliver dependable performance and good value for installers who can accommodate the non-stainless finish.

Frequently Asked Questions

Can these screws cut threads in thin steel plate?
Yes, the Type F point is designed to form threads in wood and thin plate steel; customers reported successful use with 1/4 in plate in typical trailer applications.

Will the heads strip easily?
The star drive T-40 significantly reduces slippage and stripping when used with the correct bit and proper driver technique.

Are these screws suitable for marine use?
They have a black phosphate and oil coating for corrosion resistance but are not stainless; for constant saltwater exposure a stainless fastener is recommended.