Metric A4 (316) Stainless Steel Hex Tap Bolts
A4 stainless steel hex tap bolts combine the structural advantages of a partial thread design with the superior corrosion resistance needed for marine, chemical, and high-humidity environments. Manufactured from 316 stainless steel, these fasteners resist chlorides, saltwater, and aggressive chemicals that would compromise standard 18-8 grades. Also known as hex cap screws or partial thread bolts, they feature a hexagonal head for standard wrench installation and an unthreaded shank section that improves shear performance and reduces stress concentration at the joint. Whether you are bolting together structural components on a commercial vessel, assembling food processing equipment that undergoes daily chemical washdown, or securing hardware on an offshore platform, A4 hex tap bolts provide the long-term joint integrity and corrosion performance the application demands.
How Hex Tap Bolts Work
Hex tap bolts thread into a tapped hole or through a clearance hole with a nut on the opposite side. The hexagonal head provides a positive drive surface for wrenches, ratchets, and sockets, allowing high installation torque without cam-out. What distinguishes a tap bolt from a fully threaded bolt is the unthreaded shank section directly below the head. This smooth shank acts as a dowel pin within the joint, carrying shear loads through the solid bolt body rather than across the threads. The result is improved fatigue resistance, better load distribution, and stronger performance in applications where lateral forces act on the fastened connection. Thread engagement begins only within the tapped hole or nut, keeping the highest-stress clamping zone free of thread root stress risers.
Why Choose A4 (316) Stainless Steel
A4 stainless steel, also known as 316 stainless, contains molybdenum that significantly improves resistance to pitting and crevice corrosion from chlorides and marine atmospheres. Where standard A2 (18-8) stainless may develop surface corrosion in saltwater or chemical environments, A4 grade maintains its integrity and appearance over extended service life. This makes A4 hex tap bolts the preferred choice for applications where fastener replacement is difficult or costly, and where contamination from corroding hardware is unacceptable. The higher nickel and molybdenum content also provides better performance at elevated temperatures compared to standard austenitic grades.
Material Specifications
These hex tap bolts are manufactured to DIN 931 standards from A4 (316) stainless steel. The 316 designation indicates a minimum chromium content of 16%, nickel content of 10%, and the addition of 2% molybdenum for enhanced corrosion performance. A4 stainless provides tensile strength in the range of 500–700 MPa, suitable for the structural and mechanical connections where hex tap bolts are typically deployed. The material is non-magnetic in its annealed state and maintains corrosion resistance across a broad temperature range, making it appropriate for both cryogenic and moderately elevated temperature environments.
A4 (316) vs. A2 (18-8) Stainless Steel
Both A4 and A2 stainless steels are austenitic grades with excellent general corrosion resistance, but A4 provides significantly better performance in chloride-rich and chemically aggressive environments. A2 (304/18-8) stainless is the more economical option and performs well in most indoor and mild outdoor applications. A4 (316) stainless is the upgrade choice when fasteners will be exposed to saltwater, coastal air, chemical processing agents, or sustained high-humidity conditions where the added molybdenum content justifies the higher material cost. For marine, food processing, pharmaceutical, and chemical plant applications, A4 hex tap bolts are the industry-standard specification.
Common Applications
- Marine & Coastal – Structural bolting on boats, docks, offshore platforms, seawalls, and desalination equipment exposed to saltwater and coastal atmospheres
- Food & Beverage Processing – Securing frames, guards, and equipment mounts on washdown-rated processing lines where hygiene and corrosion resistance are essential
- Chemical & Pharmaceutical – Bolting together piping supports, structural frames, and equipment mounts in chemical plants, laboratories, and pharmaceutical manufacturing
- Medical & Laboratory – Structural connections in medical equipment, cleanroom fixtures, and laboratory installations requiring corrosion-free surfaces
- Construction & Infrastructure – Structural steel connections in coastal, waterfront, and industrial zones with elevated chloride or chemical exposure
- Industrial & Manufacturing – General structural and machinery assembly in humid, wet, or chemically aggressive factory environments
- OEM & Custom Fabrication – Specifying marine-grade hex tap bolts for custom equipment, enclosures, and structures designed for corrosive or outdoor deployment
Available Sizes
Albany County Fasteners stocks A4 (316) stainless steel hex tap bolts across a range of metric diameters and lengths to accommodate everything from light-duty equipment assembly to heavy structural marine connections. Sizes follow standard DIN 931 metric coarse thread specifications. Browse the listings above to find the specific diameter and length combination for your application.
Need help selecting the right A4 stainless hex tap bolt for your project? With over 18 million fasteners in stock and competitive bulk pricing, Albany County Fasteners is ready to help. Contact our team for technical assistance, volume quotes, or to discuss your marine-grade bolting requirements.