Fasteners · ASME B18.6.3 · DIN 84 / 963 (legacy DIN)
Machine Screw — ASME B18.6.3
Machine screw — a small-diameter screw for equipment assembly. Machine screws assemble instruments, panels and equipment. Pan, countersunk and cheese heads.
- ASME B18.6.3
- 18 grades
- EN 10204 3.1 / 3.2
Reviewed by the Kanak Steel & Engineering Co. technical team · Updated October 2026
What is a machine screw?
Short answer
A machine screw is a small-diameter screw for equipment assembly. Machine screws assemble instruments, panels and equipment. Pan, countersunk and cheese heads.
Machine Screw: What to Know Before Ordering
- Pan, flat and cheese heads
- Slotted or Phillips
- M2 – M10 typical
Machine Screw Materials & Grades
| Grade | Material standard | Best for |
|---|---|---|
| Inconel 825 machine screw | Finished fastener specification not asserted; material/feedstock may be supplied to ASTM B425 (UNS N08825), where applicable; manufacturing route and finished fastener requirements are to the purchase specification or project drawing | Sulphuric and phosphoric acid service, chloride stress-corrosion cracking and sour gas |
| SS 904L machine screw | Finished fastener specification not asserted; material/feedstock may be supplied to ASTM A479 (UNS N08904), where applicable; manufacturing route and finished fastener requirements are to the purchase specification or project drawing | Dilute sulphuric acid, phosphoric acid and chloride-bearing cooling water |
| SS 304 machine screw | Finished fastener specification not asserted; UNS S30400 material — requirements to the purchase specification or project drawing | General corrosion resistance, food, water and architectural work |
| SS 304L machine screw | Finished fastener specification not asserted; UNS S30403 material — requirements to the purchase specification or project drawing | Welded tanks, piping and vessels in general corrosive service |
| SS 310 / 310S machine screw | Finished fastener specification not asserted; material/feedstock may be supplied to ASTM A276 / A479 (UNS S31008), where applicable; manufacturing route and finished fastener requirements are to the purchase specification or project drawing | Furnaces, burners and heat treatment at high temperature |
| SS 316 / 316L machine screw | Finished fastener specification not asserted; UNS S31603 material — requirements to the purchase specification or project drawing | Chloride-bearing process fluids, marine air and pharmaceutical service |
| SS 321 machine screw | Finished fastener specification not asserted; UNS S32100 material — requirements to the purchase specification or project drawing | High-temperature service between 425 and 815 °C |
| SS 347 machine screw | Finished fastener specification not asserted; UNS S34700 material — requirements to the purchase specification or project drawing | Welded high-temperature piping in refineries and power plants |
| Duplex 2205 machine screw | Finished fastener specification not asserted; material/feedstock may be supplied to ASTM A276 / A479 (UNS S32205), where applicable; manufacturing route and finished fastener requirements are to the purchase specification or project drawing | Strength with chloride resistance at a stainless-steel budget |
| Super Duplex 2507 machine screw | Finished fastener specification not asserted; material/feedstock may be supplied to ASTM A276 / A479 (UNS S32750), where applicable; manufacturing route and finished fastener requirements are to the purchase specification or project drawing | Seawater and high-chloride service where strength also matters |
| Inconel 600 machine screw | Finished fastener specification not asserted; material/feedstock may be supplied to ASTM B166 (UNS N06600), where applicable; manufacturing route and finished fastener requirements are to the purchase specification or project drawing | High-temperature oxidation, caustic and nuclear service |
| Inconel 625 machine screw | Finished fastener specification not asserted; material/feedstock may be supplied to ASTM B446 (UNS N06625), where applicable; manufacturing route and finished fastener requirements are to the purchase specification or project drawing | Seawater, high strength and high temperature in one alloy |
| Inconel 718 machine screw | Finished fastener specification not asserted; material/feedstock may be supplied to ASTM B637 (UNS N07718), where applicable; manufacturing route and finished fastener requirements are to the purchase specification or project drawing | Very high strength at temperatures up to about 650 °C |
| Incoloy 800 / 800H / 800HT machine screw | Finished fastener specification not asserted; material/feedstock may be supplied to ASTM B408 (UNS N08800), where applicable; manufacturing route and finished fastener requirements are to the purchase specification or project drawing | Furnaces, petrochemical heaters and high-temperature piping |
| Hastelloy C276 machine screw | Finished fastener specification not asserted; material/feedstock may be supplied to ASTM B574 (UNS N10276), where applicable; manufacturing route and finished fastener requirements are to the purchase specification or project drawing | The most aggressive mixed acids, wet chlorine and hypochlorite |
| Hastelloy C22 machine screw | Finished fastener specification not asserted; material/feedstock may be supplied to ASTM B574 (UNS N06022), where applicable; manufacturing route and finished fastener requirements are to the purchase specification or project drawing | Mixed oxidising and reducing acids, and weld overlays |
| Monel 400 machine screw | Finished fastener specification not asserted; material/feedstock may be supplied to ASTM B164 (UNS N04400), where applicable; manufacturing route and finished fastener requirements are to the purchase specification or project drawing | Seawater, hydrofluoric acid and marine service |
| Monel K500 machine screw | Finished fastener specification not asserted; material/feedstock may be supplied to ASTM B865 (UNS N05500), where applicable; manufacturing route and finished fastener requirements are to the purchase specification or project drawing | High-strength pump shafts, bolting and springs in seawater |
Other fasteners
Stud boltA fully threaded rod supplied with two heavy hex nuts.Hex boltA bolt with a hexagonal head.Heavy hex nutA thicker and wider hexagon nut for pressure bolting.Hex nutA standard hexagon nut.WasherA flat or spring ring that spreads bolt load.Threaded rodA continuously threaded bar cut to length.U-boltA U-shaped bolt for clamping pipes to supports.Eye boltA bolt with a loop head for lifting or anchoring.Anchor boltA bolt that fixes structures or equipment to concrete.Foundation boltA heavy bolt set in concrete for machinery bases.Socket head cap screwA screw with a cylindrical head and hexagon socket.
Machine screw — questions buyers ask
What is a machine screw?
A machine screw is a small-diameter screw for equipment assembly. Machine screws assemble instruments, panels and equipment. Pan, countersunk and cheese heads.
What sizes are machine screws?
Usually small diameters, M2 to M10 or #2 to 3/8".
Which grades are machine screws available in?
Inconel 825, SS 904L, SS 304, SS 304L, SS 310 / 310S, SS 316 / 316L, SS 321, SS 347, Duplex 2205, Super Duplex 2507, Inconel 600, Inconel 625, Inconel 718, Incoloy 800 / 800H / 800HT, Hastelloy C276, Hastelloy C22, Monel 400, Monel K500.
Which standard covers machine screw dimensions?
ASME B18.6.3 · DIN 84 / 963 (legacy DIN). The material standard depends on the grade.
Reviewed by the technical team, Kanak Steel & Engineering Co.
Sources: the ASTM / ASME specifications named on this page and producer datasheets · Last updated October 2026
Sources: the ASTM / ASME specifications named on this page and producer datasheets · Last updated October 2026
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