M5 M6 M8 Phillips Countersunk Screws 304 Stainless Steel, 30–100mm

For countersunk screws, length is measured from the top of the flat head to the tip. A general rule is to choose a length equal to the thickness of the material being fastened plus at least 1.5× the screw diameter of thread engagement in the receiving material. For example, fastening a 10mm panel into a substrate with M6 screws would typically call for a 25–30mm screw. Always pre-drill and countersink to the correct 90° angle for a flush finish. Quick inch reference: 30mm ≈ 1-3/16" | 50mm ≈ 2" | 75mm ≈ 3" | 100mm ≈ 4".

The number refers to the nominal thread diameter: M5 = 5mm (≈3/16"), M6 = 6mm (≈1/4"), M8 = 8mm (≈5/16"). Each size also has a different thread pitch — M5 is typically 0.8mm, M6 is 1.0mm, and M8 is 1.25mm. Choose the size that matches your pre-tapped hole, threaded insert, or nut. M5 is common in electronics and light fixtures; M6 is widely used in furniture and machinery; M8 is typical for heavier structural assemblies.

304 stainless steel machine screws generally correspond to property class A2-70, with a tensile strength of approximately 700 MPa. This is suitable for light-to-medium duty fastening in non-structural assemblies such as furniture, cabinetry, panels, and enclosures. For high-load or structural applications, consult an engineer and consider higher-grade fasteners.

304 stainless steel offers good corrosion resistance in most outdoor environments, including rain and humidity. It is generally suitable for exterior woodwork, outdoor furniture, and light structural applications. For marine environments or areas with high salt exposure, 316 (A4) stainless steel is typically recommended instead, as 304 can show surface staining in prolonged saltwater contact.

All three sizes use ISO metric coarse thread per ISO 68-1: M5 at 0.8mm pitch, M6 at 1.0mm pitch, and M8 at 1.25mm pitch. They are compatible with standard metric nuts, threaded inserts, and tapped holes of the corresponding size. They are not compatible with UNC or UNF (imperial) threads. Always verify the thread specification of your receiving component before ordering.

M5 screws typically use a PH2 (Phillips #2) bit. M6 and M8 screws generally use a PH3 (Phillips #3) bit. Using the correct bit size is important to avoid cam-out and damage to the drive recess. A power driver with adjustable torque control is recommended for consistent, clean installation — especially in softer materials where over-torquing can strip the countersink.

Divide the mm value by 25.4. Quick reference: 8mm ≈ 5/16" | 10mm ≈ 3/8" | 12mm ≈ 1/2" | 16mm ≈ 5/8" | 20mm ≈ 13/16" | 25mm ≈ 1" | 30mm ≈ 1-3/16" | 40mm ≈ 1-9/16" | 50mm ≈ 2" | 60mm ≈ 2-3/8" | 70mm ≈ 2-3/4" | 80mm ≈ 3-1/8" | 90mm ≈ 3-9/16" | 100mm ≈ 4".

Choose based on the pre-drilled or tapped hole size in your material. M5 is commonly used in electronics enclosures, light fixtures, and thin-panel assemblies. M6 is the most versatile size and is widely used in furniture, cabinetry, and general machinery. M8 is suited for heavier assemblies, outdoor structures, and applications requiring greater clamping force. Always match the screw size to the existing thread or nut specification — do not force a different size.