Fasteners · ASME B18.2.2
Heavy Hex Nut — ASME B18.2.2
Heavy hex nut — a thicker and wider hexagon nut for pressure bolting. Heavy hex nuts go with stud bolts on flanges. They spread load better and resist thread stripping at high preload. Made to ASME B18.2.2.
- ASME B18.2.2
- 18 grades
- EN 10204 3.1 / 3.2
Reviewed by the Kanak Steel & Engineering Co. technical team · Updated October 2026
What is a heavy hex nut?
Short answer
A heavy hex nut is a thicker and wider hexagon nut for pressure bolting. Heavy hex nuts go with stud bolts on flanges. They spread load better and resist thread stripping at high preload. Made to ASME B18.2.2.
Heavy Hex Nut: What to Know Before Ordering
- Thicker than standard hex nuts
- ASME B18.2.2
- Paired with A193 studs
Heavy Hex Nut Materials & Grades
| Grade | Material standard | Best for |
|---|---|---|
| Inconel 825 heavy hex nut | Finished 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 drawing | Sulphuric and phosphoric acid service, chloride stress-corrosion cracking and sour gas |
| SS 904L heavy hex nut | Finished 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 drawing | Dilute sulphuric acid, phosphoric acid and chloride-bearing cooling water |
| SS 304 heavy hex nut | ASTM A194 8 where specified; confirm grade and class in the purchase specification | General corrosion resistance, food, water and architectural work |
| SS 304L heavy hex nut | ASTM A194 8 where specified; confirm grade and class in the purchase specification | Welded tanks, piping and vessels in general corrosive service |
| SS 310 / 310S heavy hex nut | Finished 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 drawing | Furnaces, burners and heat treatment at high temperature |
| SS 316 / 316L heavy hex nut | ASTM A194 8M where specified; confirm grade and class in the purchase specification | Chloride-bearing process fluids, marine air and pharmaceutical service |
| SS 321 heavy hex nut | ASTM A194 8T where specified; confirm grade and class in the purchase specification | High-temperature service between 425 and 815 °C |
| SS 347 heavy hex nut | ASTM A194 8C where specified; confirm grade and class in the purchase specification | Welded high-temperature piping in refineries and power plants |
| Duplex 2205 heavy hex nut | ASTM A1082 (S32205) where specified — nuts furnished when specified; otherwise may be machined from ASTM A276 / A479 bar (UNS S32205), where applicable — finished requirements to the purchase specification or project drawing | Strength with chloride resistance at a stainless-steel budget |
| Super Duplex 2507 heavy hex nut | ASTM A1082 (S32750) where specified — nuts furnished when specified; otherwise may be machined from ASTM A276 / A479 bar (UNS S32750), where applicable — finished requirements to the purchase specification or project drawing | Seawater and high-chloride service where strength also matters |
| Inconel 600 heavy hex nut | Finished 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 drawing | High-temperature oxidation, caustic and nuclear service |
| Inconel 625 heavy hex nut | ASTM F467 (N06625) where specified, 0.250–1.500 in.; otherwise may be machined from ASTM B446 bar (UNS N06625), where applicable — finished requirements to the purchase specification or project drawing | Seawater, high strength and high temperature in one alloy |
| Inconel 718 heavy hex nut | Finished fastener specification not asserted; may be machined from ASTM B637 bar (UNS N07718), where applicable; 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 heavy hex nut | Finished 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 drawing | Furnaces, petrochemical heaters and high-temperature piping |
| Hastelloy C276 heavy hex nut | ASTM F467 (N10276) where specified, 0.250–1.500 in.; otherwise may be machined from ASTM B574 bar (UNS N10276), where applicable — finished requirements to the purchase specification or project drawing | The most aggressive mixed acids, wet chlorine and hypochlorite |
| Hastelloy C22 heavy hex nut | Finished 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 drawing | Mixed oxidising and reducing acids, and weld overlays |
| Monel 400 heavy hex nut | ASTM F467 (N04400) where specified, 0.250–1.500 in.; otherwise may be machined from ASTM B164 bar (UNS N04400), where applicable — finished requirements to the purchase specification or project drawing | Seawater, hydrofluoric acid and marine service |
| Monel K500 heavy hex nut | ASTM F467 (N05500) where specified, 0.250–1.500 in.; otherwise may be machined from ASTM B865 bar (UNS N05500), where applicable — finished requirements 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.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 screwA small-diameter screw for equipment assembly.
Heavy hex nut — questions buyers ask
What is a heavy hex nut?
A heavy hex nut is a thicker and wider hexagon nut for pressure bolting. Heavy hex nuts go with stud bolts on flanges. They spread load better and resist thread stripping at high preload. Made to ASME B18.2.2.
Why use heavy hex nuts on flanges?
They provide more thread engagement and bearing area for the high preload flange joints need.
Which grades are heavy hex nuts 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 heavy hex nut dimensions?
ASME B18.2.2. 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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