Attribute Schema Library
Attribute schemafastener distribution

Hex Nut Attributes and Specifications

A hex nut is a six-sided internally threaded fastener that develops clamp load against a mating bolt or stud. Distributors sell them into four rough demand pools: structural steel (A563 DH or A194 2H heavy hex against ASTM F3125 assemblies), flange and pressure bolting, OEM lines buying to a print, and MRO counter business. The buyer is rarely browsing. They have a bolt in hand and need the nut that goes with it.

The data is hard for two structural reasons. First, three dimensional standards run in parallel and disagree. ASME B18.2.2, DIN 934, and ISO 4032 specify different widths across flats at M10, M12, M14, and M22 — and two unrelated strength scales both use the number 8: SAE J995 Grade 8 (inch, 150 ksi proof load stress) and ISO 898-2 Class 8 (metric, nearer inch Grade 5).

Second, the facts that decide the sale — thread allowance for coating, mating bolt spec, melt origin — are not stamped on the part. They live in the mill cert and the supplier datasheet, while the line item that reaches the PIM is a part number and a 40-character description.

Core

Every SKU needs these. Without them the record is not a product, it is a row.

Nut Style
enum
Heavy Hex

Same thread size, different across-flats, height, and load rating. Style is the first facet a buyer sets and the field that separates near-duplicate SKUs.

Dia./Thread Size (Nominal)
text
1/2-13

The join key to the mating bolt. Every downstream filter, cross-reference, and substitution lookup keys off this string.

Thread Series / Pitch
enum
UNC

UNC and UNF at the same nominal diameter do not interchange. 8-UN is specified above 1 in for flange work to spread load across more threads.

Material
enum
Medium carbon steel, quenched and tempered

Sets corrosion behavior, galling risk against stainless bolts, and temperature ceiling. Drives which grade scale even applies to the part.

Grade / Property Class
enum
ASTM A563 Grade DH

The strength statement. Must be stored qualified by its issuing standard — an unqualified '8' is two different parts.

Finish / Coating
enum
Hot-dip galvanized (ASTM F2329)

Corrosion class, and it changes the thread. HDG per F2329 deposits enough zinc that the nut must be tapped oversize to assemble.

Width Across Flats
number · in
7/8 in

Wrench and socket size, and the practical tell for heavy hex vs finished hex. Also decides clearance in a tight bolt pattern.

Nut Height (Thickness)
number · in
31/64 in

Thread engagement, and the only dimension separating a jam nut from a finished nut at the same across-flats.

Manufacturer Part Number
identifier
HHNDH050HDG

Cross-reference spine for competitor lookup, punchout catalogs, and customer part-number mapping.

Differentiating

What buyers actually compare on. This is where catalogs win or lose the filter.

Thread Class of Fit
enum
2B

2B is the default; 3B is a precision order; 6G exists to clear coating on metric threads. Buyers who need non-2B cannot filter for it.

Thread Direction
enum
Right hand

Left-hand thread is a distinct part with no visual tell in a photo. Without the field, LH stock is unfindable and ships wrong.

Proof Load Stress
number · psi
175,000 psi (A563 DH, 1/2-13)

The number the engineer checks. Determines whether the nut can develop the mating bolt's specified pretension before it strips.

Overtapped for Coating
boolean
Yes — tapped oversize after HDG per ASTM F2329

Whether threads were tapped oversize per the coating spec. Pairing an overtapped nut with a plain bolt loses engagement; the reverse won't assemble.

Mating Bolt Specification
text
ASTM F3125 Grade A325

Buyers shop by the bolt they hold, not the nut grade. This is the field that answers 'what nut goes on an A325?' without a phone call.

Hardness
range · HBW
248-327 HBW (A194 2H, to 1-1/2 in)

Incoming inspection checks it against the grade. Distinguishes a heat-treated nut from a look-alike that was never quenched and tempered.

Compliance & identifiers

Standards, regulatory data, and the identifiers channels reject you for missing.

Dimensional Standard
enum
ASME B18.2.2

ASME B18.2.2, DIN 934, and ISO 4032 give different across-flats at the same nominal size. Without it, dimensions are unverifiable.

Country of Melt and Manufacture
enum
Melted and manufactured in USA

DFARS 252.225-7008 turns on where specialty metal was melted, not where the nut was tapped. Two separate facts, commonly stored as one.

Certification Available
enum
MTR, lot traceable (EN 10204 3.1)

Whether a lot-traceable cert can be pulled at order time. Decides bid eligibility before price is ever discussed.

The fields that aren't in the schema at all

What most hex nuts catalogs are missing.

The table above is the schema most catalogs already have. These are the attributes that usually aren't in it — each one surfaced by a signal from the live market rather than by an audit of what's already there. This is what Anglera's Schema Foundry does on a real catalog, in this category.

Competitor signal
+ Overtapped for Coating (Thread Allowance)

Structural specialists state whether the nut is tapped oversize for a galvanized bolt. General MRO catalogs carry 'Hot-Dip Galvanized' as a finish value and expose no thread-allowance field.

A standard-tapped nut ships against an HDG bolt and will not run down on site. The crew stops, the nut comes back, and the joint gets re-sourced against a schedule.

Search signal
+ Mating Bolt Specification

Buyers search 'nut for A325 bolt' or 'A490 nut'. A catalog indexed on nut grade alone returns nothing for the query the buyer actually types, because the nut is called A563 DH.

The RFQ goes to whoever answers the mating question first. In the joint, an under-matched nut can strip before the bolt reaches specified pretension.

Competitor signal
+ Certification Availability and Melt Origin

Fastener specialists let buyers filter on domestic melt and cert availability. Most distributor records bury country of origin in a PDF and say nothing about whether a cert exists for the lot.

DoD, nuclear, and DOT bids are non-responsive without documented melt origin. Stock that cannot produce a lot-traceable cert gets rejected at receiving.

Marketplace signal
+ Nut Height (Thickness)

Jam, finished, and heavy hex at one thread size arrive from suppliers sharing near-identical description strings. With no height field, the three read as duplicates on the shelf and on the site.

A jam nut ships where a finished nut was ordered. It cannot develop the bolt's proof load, so the joint is under-clamped and nobody finds out until it backs off.

Supplier signal
+ Thread Class of Fit

Supplier datasheets state Class 2B or 6H on the drawing; the catalog record inherits neither. Buyers needing 3B, or 6G for a coated assembly, cannot filter and open a ticket instead.

Precision and coated-thread orders get quoted by hand. 3B inventory that exists sits invisible beside 2B at the same price and never gets picked.

How Schema Foundry finds these

Messy in, governed out.

The same value, spelled every way fastener distribution suppliers spell it. A filter only works once they agree.

Grade / Property Class
GR 8Grade 8G8Gr.8Class 88
SAE J995 Grade 8

Inch Grade 8 is 150 ksi proof. ISO 898-2 Class 8 is metric and nearer inch Grade 5. An unqualified '8' merges two strength classes.

Finish / Coating
HDGHot Dip GalvHot-Dipped GalvanizedGalvZinc, Hot DipG
Hot-Dip Galvanized (ASTM F2329)

Suppliers also write 'Galvanized' for electroplated zinc — a different corrosion class and a different thread allowance.

Dia./Thread Size
1/2-131/2"-13 UNC.500-131/2 in.-13 UNC-2B0.5-13
1/2-13 UNC

This string is the join key to the bolt. Free-text variants fragment the facet and break cross-reference against competitor part numbers.

Nut Style
Finished HexHex Nut, FinishedFHNHex Full NutStandard HexHex Nut Reg
Finished Hex Nut

'Full nut' is EU usage for standard height. Left unnormalized, finished and jam nuts land in the same bucket.

What buyers ask

Every one of these should be answerable from the attributes above. If it isn't, that's a gap.

  • Which nut goes with an A325 structural bolt — is A194 2H OK instead of A563 DH?
  • Is this nut overtapped so it will actually run down a hot-dip galvanized bolt?
  • Is this Grade 8 inch or Class 8 metric? They are not the same strength.
  • What is the width across flats — what socket do I need for it?
  • What is the difference between a finished hex, a heavy hex, and a jam nut in 1/2-13?
  • Can you supply a mill test report and certify domestic melt for this lot?
  • Do you stock this thread size in left-hand thread?
  • Is this 2B or 3B? My print calls out 3B.

What channels require

The same SKU, different mandatory fields per destination.

Distributor's own site (faceted search)
Nut StyleDia./Thread Size (normalized)Thread Series / PitchMaterialGrade / Property ClassFinish / Coating
Amazon Business
GTIN/UPCBrand + Manufacturer Part NumberDia./Thread SizeMaterialFinish / CoatingPack Quantity (unit count)
Ariba / Coupa punchout and CIF catalog
UNSPSC codeManufacturer Part NumberUnit of MeasurePack QuantityCountry of Origin
DLA DIBBS / government RFQ
NSNCAGE codeDimensional standard citedCountry of melt (DFARS 252.225-7008)Mill Test Report / CoC

Hex Nuts data, in practice

Is ASTM A194 Grade 2H interchangeable with ASTM A563 Grade DH?

Often, but it is a recorded fact, not an inference. Both are heavy hex to ASME B18.2.2 dimensions, and RCSC permits A563 DH/DH3 or A194 2H in F3125 (A325/A490) assemblies. A194 is written for high-pressure and high-temperature service: 2H is quenched and tempered with a minimum 850°F temper and runs 248-327 HBW up to 1-1/2 in. A563 is written for general structural and mechanical use. Where the substitution is allowed it runs one direction only, and galvanized joints still require the nut tapped oversize per F2329 either way. Store the mating spec as its own field rather than letting a counter rep infer it.

Why do hot-dip galvanized nuts have to be tapped oversize?

Hot-dip galvanizing per ASTM F2329 adds zinc to the bolt's threads, increasing their effective diameter. The nut's threads cannot grow to match, so A563 requires HDG nuts be tapped after coating, oversize by the diametral allowance in the standard's table. Because overtapping reduces thread engagement, A563 requires those nuts to be proof-load tested after coating and the assembly to be lubricated. Mechanically deposited zinc per B695 is handled differently — tapped oversize before coating, no retap. This is why 'Hot-Dip Galvanized' as a finish value under-specifies the SKU: the finish changed the thread, and the thread is what the buyer is buying.

Is Grade 8 the same as Class 8?

No, and suppliers ship both labeled '8'. Grade 8 is SAE J995, inch series, 150,000 psi proof load stress, marked with six circumferential lines 60 degrees apart plus a manufacturer's mark. Class 8 is ISO 898-2, metric, and sits closer to inch Grade 5 in strength; metric Class 10 is the nearer analogue to inch Grade 8. If both land in one enum, a Class 8 nut can be picked against a Grade 8 requisition and nothing in the record flags it. Governed values should always carry the issuing standard: 'SAE J995 Grade 8' and 'ISO 898-2 Class 8' are unambiguous where '8' is not.

What separates a finished hex, heavy hex, and jam nut in the same thread size?

Width across flats and height, per ASME B18.2.2. At 1/2-13: finished hex is 3/4 in across flats by 7/16 in thick; heavy hex is 7/8 in by 31/64 in; hex jam is 3/4 in by 5/16 in. Heavy hex spreads load over a larger bearing face and is the structural default. Jam nuts are thinner and cannot develop the mating bolt's full proof load — they lock, they do not clamp. Three different parts, one thread size. If the record carries thread size and grade but no height, they collapse into a single apparent SKU and the picker decides which one ships.

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