Standard Machine Screws
What Are Standard Machine Screws?
Standard machine screws are straight, uniform-diameter screws designed to be used with a nut or a tapped hole in metal, plastic (with inserts), or prepared wood. They’re stocked in multiple head styles, drive types, materials, and finishes for production assembly, maintenance, and OEM work.
Head & Drive Options
- Heads: pan, flat (countersunk), button, oval, truss, and round.
- Drives: slotted, Phillips, combo, Torx/6-lobe, Pozidriv (where specified), and hex-socket.
- Choose by application: flat heads sit flush in a countersink; button/truss provide wide bearing on thin sheet; pan/round are general-purpose; hex-socket and Torx reduce cam-out at higher torque.
Materials & Finishes
- 18-8 / 304 stainless: dependable corrosion resistance for most indoor/outdoor uses.
- 316 stainless: upgraded resistance for marine or chloride exposure.
- Carbon steel, zinc plated: economical, clean appearance for dry interiors.
- Black oxide steel: matte black look; light corrosion resistance—use indoors or with protective oil.
- Brass / silicon bronze: non-magnetic, conductive, and corrosion-resistant options for electrical and architectural work.
Sizes, Threads & How to Order
Specify diameter × thread × length, e.g., #8-32 × 1-1/2″, 1/4″-20 × 2″, or M4-0.7 × 20 mm. Inch series use UNC (coarse) or UNF (fine). Common inch sizes include #2-56, #4-40, #6-32, #8-32, #10-24, #10-32, 1/4″-20, 5/16″-18, and 3/8″-16. Metric sizes commonly range from M2 to M12. Length is measured from under the head to the tip—except flat (countersunk) heads, which are measured overall.
Where Standard Machine Screws Are Used
- Metal fabrication, enclosures, sheet-metal panels, and brackets
- Electronics, appliances, HVAC, and automotive service
- Fixtures, furniture, and architectural hardware
- Plastic components with threaded inserts; wood parts with inserts or T-nuts
Installation Basics
- Match the thread size and pitch to the mating nut or tapped hole.
- For tapped holes, use the correct tap-drill size and full thread depth; for clearance holes, follow the clearance chart.
- Add flat or finish washers to spread load or protect surfaces; use lock washers, prevailing-torque nuts, or threadlocker where vibration is present.
- In plastics or thin sheet, consider thread-forming/cutting screws or install threaded inserts for stronger joints.
- Apply appropriate torque—avoid over-tightening that can strip threads or deform thin materials.
Related Hardware
- Finished machine screw nuts, keps (external-tooth) nuts, flange nuts, nylon-insert lock nuts
- Flat, fender, lock, and finishing washers
- Threaded inserts for plastic/wood, T-nuts, standoffs, and spacers
Standard Machine Screws FAQs
See the accordion below for thread selection, sizing, head/drive choices, and installation tips.
Disclaimer: This page provides general guidance. Always follow the product datasheet and applicable standards.
A uniform-diameter screw used with a nut or a tapped hole. It’s driven with a screwdriver or bit (or socket for hex-socket heads).
Terms overlap, but machine screws are typically smaller diameters and driver-installed; bolts are often larger and wrench-installed. Both can be used with a nut or tapped hole if the thread matches.
The first number is diameter; the second is threads per inch (TPI). #10-24 is coarse (UNC); #10-32 is fine (UNF). Fine threads give finer adjustment; coarse threads assemble more easily and tolerate minor damage.
Measure the major diameter with calipers and check TPI with a thread gauge (inch) or pitch (metric). Match to an existing nut/tap when possible.
From under the head to the tip. Flat (countersunk) heads are measured overall.
UNC (coarse) is most common and more forgiving in field assembly. UNF (fine) is chosen for finer adjustment, higher clamp per turn, or when mating parts are already tapped fine.
Only if the mating part isn’t tapped. If you have a tapped hole or a threaded insert, you don’t need a nut.
Flat heads sit flush in a countersink; button/truss offer wide bearing on thin sheet; pan is a versatile general-purpose choice. Select based on clearance, bearing area, and appearance.
Torx/6-lobe and hex-socket reduce cam-out and handle higher torque than Phillips. Phillips/combo are common where universal tools are needed.
Yes, with threaded inserts or T-nuts. For direct fastening into plastic or thin metal, use thread-forming/cutting screws designed for those materials.
18-8/304 and 316 are generally low-magnetic; some magnetism can appear from cold working and thread rolling.
Torque depends on size, material/grade, lubrication, and joint design. Use the product’s torque table or your engineering spec; plastics and thin sheet require lower torque.
Use flat/finish washers to protect surfaces and spread load. Use lock washers, nylon-insert nuts, or threadlocker where vibration is present.
It’s best to match materials/finishes when possible to reduce galvanic corrosion and ensure compatible strength.
Common causes are mismatched thread sizes, shallow/oversize tapped holes, or over-torque. For stainless-to-stainless assemblies, use proper lubrication to reduce galling.
Often yes if threads and drives are undamaged and the application is not safety-critical. Replace fasteners that are worn, bent, or damaged.