SPAX #9 x 3-1/4 in Exterior Flat Head Deck Wood Screws - Rust

In this review of the SPAX #9 x 3-1/4 in exterior deck screws, the bottom line is simple: these are a practical choice for builders and serious DIYers who need corrosion resistance and easier driving in treated lumber. The reviewer found the patented thread serration and 4Cut Point to noticeably reduce splitting and driving torque in many hardwood and treated-wood situations, and the included T-20+ bit and MULTIhead countersink make installation more convenient. These screws are best for exterior general construction where ground contact and pressure-treated lumber are involved, while specialty woods such as cedar or redwood should be avoided.

Key Features

• Patented thread serration: Reduces driving torque by about 40 percent and helps the screw advance faster, cutting installation time on long runs.
• 4Cut Point: Self-drilling tip minimizes the need for predrilling and reduces splitting risk in dense boards and many hardwoods.
• T-Star plus drive and included bit: Superior bit engagement with a T-20+ bit in the box reduces cam-out and keeps fasteners seating cleanly.
• HCR double barrier coating: High corrosion resistance tested for ground contact and pressure-treated lumber in exterior fresh water applications.
• MULTIhead countersink: Countersinks the head flush for a neater finish and consistent seating across decking and framing tasks.

Who It's For

These screws suit professional carpenters, deck builders, and experienced DIYers working on exterior decks, stairs, and framing using pressure-treated lumber or projects with potential ground contact. The corrosion protection and included bit make them convenient for jobs where durability and fewer tool changes matter.

Homeowners working with cedar or redwood, or those needing specialized finishes for visible furniture pieces, should consider alternatives specified for those woods. Also, casual users expecting effortless starts in every situation may encounter occasional difficulty beginning a hole on very hard or knotty boards.

Pros & Cons

Pros

• High corrosion resistance with HCR double barrier coating suitable for pressure-treated lumber and ground contact scenarios.
• Thread serration and 4Cut Point reduce splitting and lower driving torque for faster, easier installs on many boards.
• T-Star plus drive and included T-20+ bit deliver strong bit engagement and reduce cam-out.

Cons

• Some users report the screws can be hard to start in very dense or knotty wood, so a pilot hole may still be needed occasionally.
• Not recommended for cedar or redwood, limiting use for certain exterior finishes and species.

Specifications

Our Verdict

For exterior construction using pressure-treated lumber or where corrosion resistance matters, these SPAX-style #9 x 3-1/4 in screws represent strong value due to reduced driving torque, a self-drilling tip, and an included T-20+ bit. They are a solid pick for deck builders and contractors, though those working mainly with cedar, redwood, or extremely knotty hardwoods should consider species-specific fasteners or predrilling in troublesome spots.

Frequently Asked Questions

Are these screws suitable for ground contact?
Yes, the HCR double barrier coating is tested and recognized for use in ground contact and pressure-treated lumber for exterior fresh water applications.

Do I need to predrill holes?
The 4Cut Point provides a self-drilling feature that often eliminates predrilling, but very dense or knotty wood may still benefit from a pilot hole.

Is a driver bit included?
Yes, a T-20+ bit is included in the box for the T-Star plus drive.