Simpson #12 x 2-1/2" Self-Drilling Hex-Washer Head Screw in 305 Stainless Steel is engineered for reliable fastening in applications where corrosion resistance is critical. Crafted from Type 305 stainless steel, this self-drilling screw drives fast and clean into aluminum and fiberglass substrates without requiring a pre-drilled pilot hole - saving time and reducing steps on the job. The indented hex-washer head provides a broad bearing surface and a secure grip during installation, while the #3 drill point penetrates material cleanly for a flush, professional finish. Whether you are working on marine trim, exterior panels, fiberglass enclosures, or aluminum framing, this Simpson stainless fastener delivers dependable holding strength in environments where standard carbon steel screws would corrode and fail.

Key Features

• Type 305 Stainless Steel construction - provides strong corrosion resistance for use in humid, wet, and outdoor environments where standard steel fasteners would rust prematurely
• Self-drilling #3 drill point - eliminates the need for a pilot hole, speeding up installation in aluminum and fiberglass applications and reducing the number of tools required on site
• Indented hex-washer head with 5/16 in. hex drive - delivers a wide bearing surface that distributes clamping load evenly and resists pull-through, while the hex drive allows high torque with minimal cam-out
• Tapping screw thread at 14 TPI - cuts its own mating thread into the base material for a tight, vibration-resistant connection that holds securely over time
• #12 diameter at 2-1/2 in. length - offers substantial fastening depth and shank strength suited to thicker aluminum panels, fiberglass sheets, and structural assemblies where shorter fasteners may not provide adequate grip
• Simpson brand quality - backed by a manufacturer with a strong reputation in structural fastening, giving contractors and builders confidence in consistent dimensional accuracy and performance

Why This Product

• Designed specifically for aluminum and fiberglass - not steel: the #3 drill point and 305 stainless material combination is optimized for non-ferrous and composite substrates, giving you a fastener that works correctly the first time without spinning out or galling
• No pilot hole required: the self-drilling tip bores and fastens in a single step, cutting labor time on repetitive fastening tasks such as attaching aluminum trim, fiberglass panels, or marine-grade enclosures
• Corrosion-resistant stainless steel for long service life: Type 305 stainless resists oxidation and surface degradation in moisture-exposed and outdoor environments, helping prevent the rust staining and structural weakening that carbon steel fasteners cause over time
• Hex-washer head for high-torque driving: the 5/16 in. hex drive works with standard nut drivers and impact drivers, allowing fast, consistent installation without the slippage associated with Phillips or slotted drive styles

Specifications

• Brand: Simpson Strong-Tie
• Screw Size: #12
• Length: 2-1/2 in.
• Coating/Material: Type 305 Stainless Steel
• Drive Type: 5/16 in. Hex
• Head Type: Hex Washer Head (Indented)
• Thread Type: Tapping
• TPI: 14
• Point Type: #3 Drill Point
• Country of Origin: Taiwan

Available Pack Options

• S12250HDUC: 100 Pk
• S12250HDUM: 1000 Pk

Approved Applications

• Aluminum panel and framing fastening
• Fiberglass sheet and enclosure attachment
• Exterior and marine trim installation
• Non-ferrous substrate fastening where corrosion resistance is required

Frequently Asked Questions

Can this screw be used to fasten into steel?

No. This screw is designed for aluminum and fiberglass fastening only, not steel. Using it in steel substrates is outside its intended application and may result in inadequate holding strength or fastener damage.

Do I need to drill a pilot hole before driving this screw?

No pilot hole is required. The #3 drill point is self-drilling, meaning it bores its own entry hole as it is driven - allowing you to fasten directly into aluminum or fiberglass in a single step.

What type of driver do I need for this screw?

This screw uses a 5/16 in. hex drive. A standard 5/16 in. nut driver bit or hex socket, compatible with most drills and impact drivers, is all that is needed to drive and seat the screw securely.

Why is 305 stainless steel used instead of carbon steel for this application?

Type 305 stainless steel provides corrosion resistance that carbon steel cannot match in wet, humid, or outdoor environments. It prevents rust staining on aluminum and fiberglass surfaces and maintains fastener integrity over time in conditions where carbon steel fasteners would corrode and weaken.

Note: Product dimensions and/or thread length may differ from picture. Please see the item description above for specifications.