M4 M5 M6 Square Head Bolts Full Threaded – A2 304 Stainless Steel

Generally, the bolt length should equal the total thickness of all materials being clamped, plus enough thread to fully engage the nut (typically 1–1.5× the bolt diameter). For example, clamping 20mm of material with an M5 bolt typically requires a length of at least 25–30mm. Available lengths range from 8mm (≈5/16") to 60mm (≈2-3/8"). When in doubt, choose the next longer size — excess thread can always be accommodated with a washer or lock nut.

These bolts are made from A2 304 stainless steel and are rated at Grade 6.8, which typically provides a tensile strength of around 600 MPa and a proof load of approximately 480 MPa. In practice, the actual load capacity depends on the specific diameter, length, and installation conditions. For safety-critical structural applications, always consult an engineer and verify load requirements against the specific bolt size.

A2 304 stainless steel generally offers good corrosion resistance and is suitable for outdoor use, including exposure to rain, humidity, and mild coastal environments. For highly corrosive conditions — such as direct saltwater immersion or chemical exposure — A4 316 stainless steel is typically recommended. These bolts are not coated or plated, so their corrosion resistance comes from the base material itself.

These bolts follow the ISO metric coarse thread standard: M4 at 0.7mm pitch, M5 at 0.8mm pitch, and M6 at 1.0mm pitch. They are compatible with any standard metric nut, washer, or threaded insert of the matching size from any manufacturer. They are not compatible with UNC or UNF inch-standard hardware.

Square head bolts are driven with an open-end wrench, adjustable wrench, or a square-socket wrench sized to the head. The square profile provides four flat bearing surfaces, which generally allows higher torque application and better grip than a hex head in situations where the wrench can only engage from one direction. A socket wrench is recommended for high-torque applications.

The thread diameter should match the existing threaded hole, nut, or insert in your application. As a general guide: M4 is typically used for light-duty fastening in electronics, small fixtures, and thin sheet metal; M5 is common in medium-duty machinery, furniture, and structural brackets; M6 is used for heavier structural connections, automotive components, and industrial equipment. If you are tapping a new hole, choose the diameter that provides adequate shear strength for your load.

Each listing variant specifies a single size and a pack quantity of 1, 5, 10, 15, 20, 25, or 30 pieces. To order multiple sizes, simply add each size/quantity combination to your cart separately. Mixing sizes within a single variant is not supported — each variant ships as a single-size pack.