316 - Stainless steel - Hexagon socket knurled heads cap screw

Technical Advantages of A4 Knurled Screws

In offshore engineering and chemical processing, a fastener must do two things: survive the environment and be easy to install. Grade 316 socket screws excel at the former due to their alloy composition. The addition of the knurled head addresses the latter—providing a non-slip surface that allows technicians to thread the screw by hand before applying final torque with a tool, a small detail that saves significant time in the field.

Material Specifications: Grade A4 (316)

Our socket cap screws are manufactured to ISO 4762 (DIN 912) standards using high-grade austenitic steel:

The Molybdenum Factor

The defining characteristic of Grade 316 (A4) is the addition of 2-3% Molybdenum. This element creates a barrier against "pitting"—a localized form of corrosion that eats small holes into metal surfaces exposed to salt water or industrial pollution. Grade 304 lacks this element.

Mechanical Strength (A4-70)

Most of our stock is Grade A4-70. This denotes a tensile strength of minimum 700 N/mm² and a yield strength of 450 N/mm². It offers structural reliability comparable to high-tensile carbon steel but with inherent rust immunity.

Non-Magnetic Properties

While cold-working can induce slight magnetism, Grade 316 remains less magnetic than Grade 304, making it suitable for sensitive instrumentation and medical devices.

Quality Assurance

We understand that material failure in marine environments can be costly. We are happy to supply an EN 10204 3.1 Material Certificate upon request, which verifies the chemical analysis of your batch. Please note that third-party inspection services are available for an additional fee.

Critical Applications

Grade 316 knurled socket screws are the standard specification for:

• Marine Hardware: Deck fittings, cleats, and engine bay fasteners on yachts and commercial vessels.
• Chemical Plants: Securing pumps, valves, and flanges exposed to corrosive fluids.
• Sub-sea Equipment: ROVs (Remotely Operated Vehicles) and diving gear where reliability is paramount.
• Food & Pharmaceutical: Equipment requiring high sterility and resistance to aggressive cleaning agents.

Frequently Asked Questions

Why is the knurled head useful in marine applications?

In marine environments, conditions are often wet, and technicians may be wearing gloves or have slippery hands. A smooth (plain) head can be difficult to grip and spin. The knurling provides the necessary friction to start the thread manually, preventing the screw from being dropped into the bilge or water.

What is the difference between A4-70 and A4-80?

The difference is strength. A4-70 has a tensile strength of 700 N/mm², while A4-80 is cold-worked further to achieve 800 N/mm². A4-70 is the standard commercial grade suitable for most applications. A4-80 is used for high-stress structural connections. Unless specified, our A4 screws are typically A4-70.

How do I prevent 316 screws from seizing (galling)?

Stainless steel threads, especially the highly corrosion-resistant 316 grade, are prone to galling (cold welding) under high friction. To prevent this, ensure the threads are clean and always apply a high-quality anti-seize lubricant (such as nickel paste or PTFE) before installation. Tightening slowly with a hand tool rather than a high-speed impact driver also helps.