Simpson #12 x 1-1/4" Self-Drilling Hex-Washer Head Screw in 305 Stainless Steel is a precision-engineered fastener from Simpson designed for reliable, corrosion-resistant fastening in aluminum and fiberglass applications. The tapping thread design and #3 drill point allow this screw to cut its own path without a pre-drilled pilot hole, saving installation time and effort. With a 5/16 in. hex drive and indented hex-washer head, this screw delivers solid torque transfer and a secure seating surface - making it a dependable choice for contractors and builders working with non-ferrous materials in demanding environments.

Key Features

• Type 305 Stainless Steel construction - provides strong resistance to corrosion and oxidation, keeping the fastener reliable over time in moisture-exposed or outdoor environments
• Self-drilling #3 drill point - cuts through aluminum and fiberglass without a pre-drilled pilot hole, speeding up installation and reducing tool requirements on the job site
• Tapping screw thread at 14 TPI - forms its own mating threads as it drives, creating a tight, secure grip in the workpiece material
• Indented hex-washer head - distributes clamping load across a wider surface area, reducing the risk of material damage and improving pull-through resistance in thin or soft substrates
• 5/16 in. hex drive - compatible with standard hex-head drivers and nut runners for fast, high-torque installation with common tools
• #12 screw size at 1-1/4 in. length - a versatile mid-range fastener size well suited to light-gauge and panel fastening work where both strength and precision matter

Why This Product

• Optimized for aluminum and fiberglass fastening - this screw is specifically suited to non-ferrous and composite materials, making it a go-to choice for panel installation, siding, and structural trim work where galvanic compatibility matters
• Stainless steel grade keeps connections lasting longer - 305 stainless resists rust and surface degradation, reducing the need for frequent inspection or replacement in humid or wet-exposure applications
• One-step installation with the self-drilling point - the #3 drill point eliminates the pre-drilling step, cutting labor time in repetitive fastening tasks across large panel or sheet installations
• Trusted Simpson quality in a workhorse fastener - engineered to consistent tolerances from a brand recognized in the construction and fastening industry, delivering predictable performance across every fastener in the box

Specifications

• Brand: Simpson Strong-Tie
• Screw Size: #12
• Length: 1-1/4 in.
• Head Type: Hex Washer Head (Indented)
• Drive Type: 5/16 in. Hex
• Thread Type: Tapping Threads
• TPI: 14
• Point Type: #3 Drill Point
• Material/Coating: Type 305 Stainless Steel
• Country of Origin: Taiwan

Available Pack Options

• S12125HDUC: 100 Pk
• S12125HDUM: 1000 Pk

Approved Applications

• Fastening aluminum panels, sheets, and extrusions
• Securing fiberglass panels, enclosures, and composite materials
• Light-gauge non-ferrous metal fastening where corrosion resistance is required

Frequently Asked Questions

Can this screw be used to fasten into steel?

No. This screw is intended for fastening aluminum and fiberglass only - it is not rated or recommended for use in steel substrates. Using it in steel may result in inadequate engagement or fastener failure.

Does this screw require a pre-drilled pilot hole?

No. The #3 drill point is self-drilling, meaning it cuts its own entry hole as it is driven. This eliminates the need for a separate drilling step when working with aluminum and fiberglass materials.

What driver size is needed for this screw?

This screw uses a 5/16 in. hex drive. A standard 5/16 in. hex-head driver bit or nut runner attachment is compatible with most power drills and impact drivers.

Why is 305 stainless steel used for this type of fastener?

Type 305 stainless steel offers good corrosion resistance and is well suited to applications involving aluminum and fiberglass where moisture exposure or oxidation could degrade a standard steel fastener over time. It also helps minimize the risk of galvanic corrosion when used with aluminum substrates.

Note: Product dimensions and/or thread length may differ from picture. Please refer to the specifications listed above for accurate product details.