Allen Bolt

What is an Allen bolt?

An Allen bolt (also known as a socket head cap screw) is a fastener with a cylindrical head and a hexagonal internal drive, tightened using an Allen key or hex wrench. The recessed drive allows higher torque in confined spaces where standard tools cannot reach.

What materials are Allen bolts available in?

Allen bolts are available in alloy steel (Grades 8.8, 10.9, 12.9), stainless steel (A2 and A4), mild steel, and brass. For high-strength applications, Grade 12.9 alloy steel is standard. For corrosion resistance in outdoor or wet environments, A2 or A4 stainless steel is recommended.

What sizes do Allen bolts come in?

Metric Allen bolts are commonly available from M2 to M36. Imperial sizes in UNC and UNF threads are also available. The most frequently used sizes in general engineering are M3 through M20, with matching Allen key sizes ranging from 1.5 mm to 14 mm.

What is the difference between Grade 10.9 and Grade 12.9?

Grade 10.9 bolts have a minimum tensile strength of 1000 MPa and are widely used in automotive and structural assemblies. Grade 12.9 bolts offer 1200 MPa tensile strength and are suited for high-stress machinery and precision tooling where maximum clamping force is required.

What standards do Allen bolts conform to?

Most metric Allen bolts are manufactured to ISO 4762 or DIN 912, which are dimensionally interchangeable. Inch-series bolts follow ASME B18.3. Always verify the standard specified in your engineering drawing before ordering to ensure full compliance.