Zinc Plated Phillips Flat Head Machine Screws — #4-40 to #10-32, Multiple Lengths

A general rule of thumb is to select a length that is 2–3 times the thickness of the material being fastened. For example, when joining 1/4" (6mm) sheet metal or plastic panels, a 1/2" to 3/4" screw is typically appropriate. Always account for the countersink depth so the flat head sits flush with the surface. If you are threading into a nut or insert, make sure enough thread engagement remains after passing through the material — generally at least 1.5× the screw diameter in thread engagement is recommended.

These screws follow the Unified National Thread Standard used throughout the United States and Canada. #6-32 and #10-24 are UNC (coarse thread); #8-32 and #10-32 are UNF (fine thread). They are fully compatible with standard US inch-thread hex nuts, wing nuts, threaded inserts, and tapped holes of the matching size and pitch. They are not compatible with metric threads.

The zinc plating provides moderate corrosion resistance, making these screws suitable for indoor use and light-duty outdoor applications in dry or low-humidity conditions. They are generally not recommended for prolonged exposure to rain, salt spray, or marine environments. For those conditions, stainless steel fasteners are typically a better choice. If you need guidance on the right material for your environment, feel free to contact us.

These screws are designed for use with metal, hard plastic, fiberglass, and composite panels where a pre-tapped hole or matching nut is used. Common applications include electronics enclosures, electrical panels, aluminum extrusions, and plastic housings. They are not self-tapping — the receiving material must already have a properly sized threaded hole or be used with a nut or threaded insert.

Both are #10 diameter screws (approximately 0.190" / 4.8mm shank diameter), but they have different thread pitches. #10-24 has 24 threads per inch (coarse thread, UNC), while #10-32 has 32 threads per inch (fine thread, UNF). They are not interchangeable — forcing the wrong thread into a tapped hole will strip the threads. Always verify the thread pitch of your existing hole or nut before selecting a size.

A #1 Phillips bit is generally used for #4-40 and #6-32 screws, while a #2 Phillips bit is typically used for #8-32, #10-24, and #10-32 screws. Using the correct bit size is important — an undersized bit can cam out and damage the screw head, while an oversized bit may not seat properly. We recommend using a bit with a good fit and applying steady downward pressure during driving.

Zinc plated steel machine screws generally offer good tensile and shear strength for light-to-medium duty fastening applications such as panel assembly, electronics enclosures, and general fabrication. Exact load ratings depend on the base steel grade. These screws are typically not rated for primary structural or safety-critical load-bearing applications. If you need specific tensile strength data for your application, please contact us to confirm.

In most cases, flat head countersunk screws are designed to bear directly against the countersink in the material, so a washer under the head is not typically used. However, a flat washer or lock washer can be used under a nut on the opposite side of the joint to distribute load and prevent loosening, especially in vibration-prone applications. If the material is soft (such as thin plastic), a backing washer on the nut side is generally recommended.