Socket Cap Head Screws 304 Stainless Steel — M2 M3 M4 M5 M6 M8 Hex Allen Bolt

A general rule is that the screw should engage at least 1.5× the thread diameter into the receiving material. For example, an M4 screw typically needs at least 6mm of thread engagement. Add the thickness of the clamped material to get your total length. As a quick inch reference: 25mm ≈ 1", 50mm ≈ 2", 80mm ≈ 3-1/8". Lengths here range from 4mm to 80mm — select the variant that matches your application.

These screws are made from 304 stainless steel (also known as A2 stainless), which generally offers good corrosion resistance, solid tensile strength, and reliable performance across a wide temperature range. It is the most widely used stainless steel grade for general-purpose fasteners.

304 stainless steel typically performs well in most outdoor environments and resists rust in normal atmospheric conditions. For highly corrosive environments — such as marine, coastal, or chemical exposure settings — 316 stainless steel (A4 grade) is generally recommended instead. For standard outdoor furniture, garden structures, or covered exterior applications, 304 is in most cases sufficient.

Socket cap head screws use a standardized hex socket. The required Allen key size typically corresponds to the thread diameter as follows:

• M2 → 1.5mm hex key
• M3 → 2.5mm hex key
• M4 → 3mm hex key
• M5 → 4mm hex key
• M6 → 5mm hex key
• M8 → 6mm hex key

Always verify with your specific fastener before installation.

These screws use the ISO metric coarse thread standard (DIN 912 / ISO 4762 profile), which is the most widely used metric fastener standard globally. They are compatible with standard metric nuts, threaded inserts, and tapped holes of the same pitch. They are not compatible with UNC/UNF (imperial) threads.

Yes, socket cap head screws in M2–M8 are commonly used in aluminum extrusions, CNC-machined parts, and structural plastic assemblies. For softer materials such as plastic or thin aluminum, it is generally advisable to use a threaded insert (e.g., heat-set or press-fit) to maximize pull-out strength and prevent thread stripping.

Torque capacity depends on thread size and the specific application. As a general reference for 304 stainless socket cap screws:

• M3 — typically ≈ 1.0–1.3 N·m
• M4 — typically ≈ 2.5–3.0 N·m
• M5 — typically ≈ 5–6 N·m
• M6 — typically ≈ 8–10 N·m
• M8 — typically ≈ 20–25 N·m

Always consult a torque specification chart for your specific application and material combination.