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Fasteners · ASME B18.3 · ISO 4762 · DIN 912 (legacy DIN)

Socket Head Cap Screw — ASME B18.3

Socket head cap screw — a screw with a cylindrical head and hexagon socket. Allen-type cap screws are used where the head must sit flush or space is tight.

  • ASME B18.3
  • 18 grades
  • EN 10204 3.1 / 3.2

Reviewed by the Kanak Steel & Engineering Co. technical team · Updated October 2026

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What is a socket head cap screw?

Short answer

A socket head cap screw is a screw with a cylindrical head and hexagon socket. Allen-type cap screws are used where the head must sit flush or space is tight.

Standards for socket head cap screws

DimensionsASME B18.3 · ISO 4762 · DIN 912 (legacy DIN)
Material — high temperatureASTM A193 (B7, B8, B8M) with ASTM A194 nuts
Material — low temperatureASTM A320 (L7)
CertificateEN 10204 3.1, or 3.2 with third-party inspection

Socket Head Cap Screw: What to Know Before Ordering

  • Hex socket drive
  • ASME B18.3 · DIN 912
  • Metric and inch
Line drawing of a socket head cap screwLine drawing of a socket head cap screw heavy hex nutL — lengthd
TYPE · SOCKET HEAD CAP SCREWDIM · ASME B18.318 GRADESKANAK STEEL

Socket Head Cap Screw Materials & Grades

GradeMaterial standardBest for
Inconel 825 socket head cap screwFinished fastener specification not asserted; may be machined from ASTM B425 bar (UNS N08825), where applicable; finished fastener requirements are to the purchase specification or project drawingSulphuric and phosphoric acid service, chloride stress-corrosion cracking and sour gas
SS 904L socket head cap screwFinished fastener specification not asserted; may be machined from ASTM A479 bar (UNS N08904), where applicable; finished fastener requirements are to the purchase specification or project drawingDilute sulphuric acid, phosphoric acid and chloride-bearing cooling water
SS 304 socket head cap screwASTM A193 B8 where specified; confirm grade and class in the purchase specificationGeneral corrosion resistance, food, water and architectural work
SS 304L socket head cap screwASTM A193 B8 where specified; confirm grade and class in the purchase specificationWelded tanks, piping and vessels in general corrosive service
SS 310 / 310S socket head cap screwFinished fastener specification not asserted; may be machined from ASTM A276 / A479 bar (UNS S31008), where applicable; finished fastener requirements are to the purchase specification or project drawingFurnaces, burners and heat treatment at high temperature
SS 316 / 316L socket head cap screwASTM A193 B8M where specified; confirm grade and class in the purchase specificationChloride-bearing process fluids, marine air and pharmaceutical service
SS 321 socket head cap screwASTM A193 B8T where specified; confirm grade and class in the purchase specificationHigh-temperature service between 425 and 815 °C
SS 347 socket head cap screwASTM A193 B8C where specified; confirm grade and class in the purchase specificationWelded high-temperature piping in refineries and power plants
Duplex 2205 socket head cap screwASTM A1082 (S32205) where specified; otherwise may be machined from ASTM A276 / A479 bar (UNS S32205), where applicable — finished requirements to the purchase specification or project drawingStrength with chloride resistance at a stainless-steel budget
Super Duplex 2507 socket head cap screwASTM A1082 (S32750) where specified; otherwise may be machined from ASTM A276 / A479 bar (UNS S32750), where applicable — finished requirements to the purchase specification or project drawingSeawater and high-chloride service where strength also matters
Inconel 600 socket head cap screwFinished fastener specification not asserted; may be machined from ASTM B166 bar (UNS N06600), where applicable; finished fastener requirements are to the purchase specification or project drawingHigh-temperature oxidation, caustic and nuclear service
Inconel 625 socket head cap screwASTM F468 (N06625) where specified, No. 0 (0.060 in.) – 1.500 in.; otherwise may be machined from ASTM B446 bar (UNS N06625), where applicable — finished requirements to the purchase specification or project drawingSeawater, high strength and high temperature in one alloy
Inconel 718 socket head cap screwFinished fastener specification not asserted (ASTM A1014 coverage of this product type pending current standard text); may be machined from ASTM B637 bar (UNS N07718), where applicable; finished fastener requirements are to the purchase specification or project drawingVery high strength at temperatures up to about 650 °C
Incoloy 800 / 800H / 800HT socket head cap screwFinished fastener specification not asserted; may be machined from ASTM B408 bar (UNS N08800), where applicable; finished fastener requirements are to the purchase specification or project drawingFurnaces, petrochemical heaters and high-temperature piping
Hastelloy C276 socket head cap screwASTM F468 (N10276) where specified, No. 0 (0.060 in.) – 1.500 in.; otherwise may be machined from ASTM B574 bar (UNS N10276), where applicable — finished requirements to the purchase specification or project drawingThe most aggressive mixed acids, wet chlorine and hypochlorite
Hastelloy C22 socket head cap screwFinished fastener specification not asserted; may be machined from ASTM B574 bar (UNS N06022), where applicable; finished fastener requirements are to the purchase specification or project drawingMixed oxidising and reducing acids, and weld overlays
Monel 400 socket head cap screwASTM F468 (N04400) where specified, No. 0 (0.060 in.) – 1.500 in.; otherwise may be machined from ASTM B164 bar (UNS N04400), where applicable — finished requirements to the purchase specification or project drawingSeawater, hydrofluoric acid and marine service
Monel K500 socket head cap screwASTM F468 (N05500) where specified, No. 0 (0.060 in.) – 1.500 in.; otherwise may be machined from ASTM B865 bar (UNS N05500), where applicable — finished requirements to the purchase specification or project drawingHigh-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.Machine screwA small-diameter screw for equipment assembly.

Socket head cap screw — questions buyers ask

What is a socket head cap screw?

A socket head cap screw is a screw with a cylindrical head and hexagon socket. Allen-type cap screws are used where the head must sit flush or space is tight.

DIN 912 and ISO 4762 — are they the same?

Yes, ISO 4762 replaced DIN 912 with the same main dimensions.

Which grades are socket head cap 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 socket head cap screw dimensions?

ASME B18.3 · ISO 4762 · DIN 912 (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
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