Simpson #12 x 4" Self-Drilling Hex-Washer Head Screw in 316 Stainless Steel is a heavy-duty fastener engineered for reliable performance in corrosive and demanding environments. Built from Type 316 stainless steel - the grade recognized for superior resistance to saltwater, moisture, and harsh outdoor conditions - this screw is purpose-designed for securing aluminum and fiberglass assemblies where a standard fastener would quickly fail. The #3 drill point drives directly through material without pre-drilling, and the indented hex-washer head provides a strong, stable drive surface for consistent installation. Whether you're working on marine structures, architectural panels, or exterior fiberglass enclosures, this self-drilling screw delivers secure, long-lasting fastening in environments that demand corrosion-resistant hardware.

Key Features

• Type 316 Stainless Steel construction - resists corrosion from saltwater, moisture, and chemical exposure, making it the right choice for coastal, marine, and outdoor applications
• Self-drilling #3 drill point - eliminates the need for pre-drilling pilot holes, saving time and reducing steps during installation in aluminum and fiberglass
• Indented hex-washer head with 5/16 in. hex drive - distributes load across a wider bearing surface and provides a secure grip for power drivers, reducing cam-out and fastener damage
• Tapping screw threads at 14 TPI - cut clean, tight threads into material as the screw drives, creating a firm mechanical hold without pre-tapping
• 4" length with #12 diameter - provides substantial fastening depth and shank strength for heavier-gauge aluminum panels and thick fiberglass sections
• Sold individually (each) - allows you to purchase exactly what your project requires without excess inventory

Why This Product

• 316 stainless steel is specifically formulated with added molybdenum for enhanced chloride resistance - making this screw the correct specification for coastal installations, marine environments, and exterior aluminum or fiberglass assemblies where lesser grades corrode prematurely
• The combination of a self-drilling point and tapping threads means a single fastener handles both hole-forming and thread-cutting in one pass - no separate drill bit or tap required for aluminum and fiberglass work
• The hex-washer head design provides a broad clamping surface that won't pull through thin aluminum sheets or fiberglass panels, helping maintain panel integrity over time
• At #12 diameter and 4" length, this screw offers substantial holding power for thicker substrates and structural connections in non-steel applications, where a smaller or shorter fastener might work loose

Specifications

• Brand: Simpson Strong-Tie
• Screw Size: #12
• Length: 4 in.
• Material/Coating: Type 316 Stainless Steel
• Head Type: Hex Washer Head (Indented)
• Drive Type: 5/16 in. Hex
• Thread Type: Tapping Threads
• TPI: 14
• Point Type: #3 Drill Point
• Country of Origin: Taiwan

Available Pack Options

• T12400HDUC: 100 Pk
• T12400HDUM: 1000 Pk

Approved Applications

• Aluminum panel and structure fastening
• Fiberglass panel and enclosure fastening
• Marine and coastal construction assemblies requiring corrosion-resistant hardware
• Exterior architectural panels in moisture-exposed environments

Frequently Asked Questions

Can this screw be used to fasten steel?

No. This self-drilling hex-washer head screw is designed specifically for fastening aluminum and fiberglass - it is not intended for use in steel applications. For steel fastening, a different screw type and material grade would be required.

Why is 316 stainless steel important for this type of fastener?

Type 316 stainless steel contains molybdenum, which provides significantly improved resistance to chlorides and corrosive environments compared to standard 304 stainless. This makes it particularly well-suited for outdoor, marine, and coastal installations where moisture and salt exposure would cause inferior materials to corrode and fail over time.

Do I need to pre-drill a pilot hole before installing this screw?

No. The #3 drill point is self-drilling, meaning it bores its own hole as the screw is driven into aluminum or fiberglass. The tapping threads then cut into the material to create a secure hold - all in a single driving operation.

What tool do I use to drive this screw?

This screw is driven with a 5/16 in. hex (hex-washer) driver bit, compatible with standard power drills and impact drivers fitted with a 5/16 in. hex socket or nut driver attachment.

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