Attribute Schema Library
Attribute schemafastener distribution

Socket Head Cap Screws Attributes

A socket head cap screw is a cylindrical-head machine screw driven by an internal hex. Inch sizes are dimensioned by ASME B18.3 and made to ASTM A574; metric sizes follow ISO 4762 (DIN 912) with property classes from ISO 898-1. The buyers are machine builders, tool-and-die shops, OEM maintenance, and job shops — and they are almost always working from a drawing callout, not a product description.

The data is hard for three reasons. Variant explosion: one thread size crosses dozens of lengths, and every length crosses material, grade, and finish. Two spec systems collide, so the same bin arrives as "1/4-20 x 1 A574 BO" from one supplier and "M6-1.0x25 12.9 blk" from the next. And the specs that decide the sale — thread length, grip, head diameter, hex key size — live in a dimensional table inside a PDF, not in the line item the supplier sends.

Certification compounds it. Country of melt, plating bake records, and lot numbers sit on mill certs that never reach the product record, so any RFQ with a DFARS or aerospace clause falls out of the catalog and into email.

Core

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

Thread Size
enum
M8-1.25

The primary filter. Diameter plus pitch or threads-per-inch; every dimensional table lookup downstream keys off it.

Nominal Length
number · mm or in
20 mm

Measured under the head on socket head cap screws. Decides whether the screw bottoms in a blind hole or leaves usable thread engagement.

Thread Length
number · mm or in
22 mm

ASME B18.3 fully threads screws at or below basic thread length LT; longer ones carry a shank. Determines shear-joint suitability.

Material
enum
Alloy Steel

Sets corrosion behavior and the strength ceiling. Alloy steel and 18-8 stainless are not interchangeable; 18-8 tops out near 80,000 psi tensile.

Property Class / Grade
enum
12.9

The strength callout on the print. Metric uses ISO 898-1 classes; inch parts carry the material spec instead. Buyers filter here first.

Finish / Coating
enum
Black Oxide

Black oxide is a dry-environment finish only; zinc is the wet-environment default. Also shifts torque-tension and stack-up in close-tolerance holes.

Drive Size (Hex Key Across Flats)
number · mm or in
6 mm

Tells the buyer whether keys already on the floor will drive the part. Exposed as a filter on the major distributor rails.

Manufacturer Part Number
identifier
91290A150

Join key for cross-reference, competitive lookup, and customer ERP part masters. Fastener buyers search MPN more often than description.

Package Quantity
number · ea per package
100

Fasteners price and ship by box, not by each. Catalog-to-pick-face quantity mismatch is a repeat source of short shipments.

Differentiating

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

Head Diameter
number · mm or in
13.0 mm

Decides whether the head clears an existing counterbore or the shoulder it seats against. Common cause of a screw that will not install.

Head Height
number · mm or in
8.0 mm

Pairs with head diameter for counterbore depth. Also the field separating standard heads from low-head (DIN 6912) alternatives.

Grip Length (Unthreaded Shank)
number · mm or in
6.5 mm

Nominal length minus thread length. Shear joints and locating applications need shank, not thread, in the shear plane.

Minimum Tensile Strength
number · psi
180,000 psi

The number engineers size joints against. ASTM A574 alloy steel is 180,000 psi through 1/2 in and 170,000 psi at 5/8 in and larger.

Thread Class / Tolerance
enum
3A

Class 3A per ASME B1.1 and 6g metric are the SHCS defaults. Matters where the mating tap runs tight or the screw gets coated after threading.

Core Hardness
range · HRC
HRC 39-45

Drives both joint design and plating decisions. A574 runs HRC 39-45 through 1/2 in, 37-45 at 5/8 in and larger.

Compliance & identifiers

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

Dimensional Standard
enum
ISO 4762 (DIN 912)

The callout on the print. Inch parts are ASME B18.3; metric are ISO 4762 (DIN 912) or ASME B18.3.1M. Buyers key the standard verbatim into search.

Material & Mechanical Spec
enum
ASTM A574

Governs strength, hardness, and what the cert has to say. ASTM A574 for inch alloy steel, ISO 898-1 for metric, ASTM F837 for stainless.

Country of Origin
identifier
Taiwan

Required for customs, Buy American screening, and marketplace feeds. Distinct from country of melt, which lives only on the mill cert.

The fields that aren't in the schema at all

What most socket head cap screws 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
+ Grip Length / Unthreaded Shank Length

McMaster-Carr publishes thread length per SKU so a buyer can compute grip. Most distributor catalogs carry nominal length and, at best, a fully-threaded flag — no way to filter on shank.

Buyer takes a fully threaded screw for a joint needing shank in the shear plane. It installs, works loose, and returns as a quality claim, not a spec error.

Supplier signal
+ Hydrogen Embrittlement Relief (bake record)

Alloy steel SHCS runs HRC 37-45, the band where ASTM F1941 requires baking after electroplating. Zinc-plated listings almost never state whether the lot was baked or to what spec.

Safety-critical and aerospace RFQs are disqualified at quote stage. Plated high-strength stock sits because nobody in the branch will certify it.

Supplier signal
+ Country of Melt

Catalogs carry Country of Origin — where the screw was manufactured — but not country of melt. DFARS specialty metals flows down on melt, and it appears only on the mill cert.

Defense and aerospace lines drop out of automated quoting into manual cert chasing, or get no-bid outright because nobody can confirm melt source in time.

Search signal
+ Dimensional Standard Designation

Buyers type "DIN 912 M6x25 12.9" verbatim off a European print. A catalog storing only "M6-1.0 x 25mm Socket Head Cap Screw, Alloy" returns zero results for that query.

Lost site search and lost paid traffic on the exact terms buyers use. RFQ lines get keyed as no-bid because the standard cross-reference lives in a rep's head.

Review signal
+ Head Diameter and Head Height

Product Q&A fills with "will this fit my counterbore?" Head dimensions are in the ASME B18.3 and ISO 4762 tables and on supplier drawings, but rarely as filterable fields on the record.

Head fouls the counterbore or the shoulder it seats against. The part comes back after a failed install and gets written off as a wrong-part pick.

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.

Thread Size
M8-1.25M8 x 1.25M8x1.25M8 1.25mm1/4-20.250-20
M8-1.25

The primary filter. Six spellings of one size fragments the facet into six buckets, each showing a fraction of real stock.

Material / Grade
18-8A2A2-70SS304304 SSStainless 18-8
18-8 Stainless Steel

Trap: 18-8 is a material family, A2-70 is an ISO 3506-1 property class. Normalize to material; do not silently promote 18-8 to A2-70.

Finish / Coating
Black OxideBlk OxBOBlack Oxide & OilThermal Black OxideBlack Ox.
Black Oxide

Abbreviations arrive straight off supplier line items. Unnormalized, the finish facet splits and the dry-vs-wet choice gets buried.

Dimensional Standard
DIN 912DIN912ISO 4762DIN 912/ISO 4762EN ISO 4762DIN EN ISO 4762
ISO 4762

Govern to ISO 4762, keep DIN 912 as a search synonym. Buyers key DIN 912 off drawings and will for years.

What buyers ask

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

  • Is this fully threaded or does it have a shank under the head?
  • What size hex key does it take?
  • Will the head drop into a standard counterbore for this size?
  • Is Class 12.9 the same thing as Grade 8?
  • Can you send a mill cert showing country of melt for this lot?
  • My drawing calls out DIN 912 — is your ISO 4762 the same screw?
  • Is black oxide OK outdoors, or do I need zinc?
  • Do you stock A2-70, or is your 18-8 the same thing?

What channels require

The same SKU, different mandatory fields per destination.

Amazon Business
GTIN / UPCBrand + Manufacturer Part NumberThread SizeNominal LengthMaterialCountry of Origin
Distributor faceted search and site navigation
Thread SizeNominal LengthProperty Class / GradeMaterialFinish / CoatingDrive Size (Hex Key Across Flats)
Customer punchout / ERP catalog (cXML, CIF)
Manufacturer Part NumberUNSPSC codeUnit of MeasurePackage QuantityCountry of OriginShort description within field limit
Defense and aerospace RFQ / cert-gated quoting
Material & Mechanical SpecCountry of meltLot / heat numberHydrogen embrittlement relief recordDimensional Standard

Socket Head Cap Screws data, in practice

Is a Class 12.9 socket head cap screw the same as ASTM A574?

They are close in strength but they are different systems, and conflating them corrupts your data. ASTM A574 is the inch material spec for quenched-and-tempered alloy steel socket head cap screws: 180,000 psi minimum tensile through 1/2 in, 170,000 psi at 5/8 in and larger, core hardness HRC 39-45 (37-45 for 5/8 in and up). Class 12.9 is a metric property class under ISO 898-1. Dimensions come from a third place entirely — ASME B18.3 for inch, ISO 4762 or ASME B18.3.1M for metric. Keep material, property class, material spec, and dimensional standard as four separate fields. Do not auto-map "Alloy Steel" to "12.9" on inch parts; the class does not apply and the value will fail an audit.

Why carry thread length when the record already has nominal length?

Because grip is what the joint sees. ASME B18.3 defines a basic thread length LT per diameter: screws at or below LT are fully threaded, and longer screws have an unthreaded body. Grip length is roughly nominal length minus thread length. A joint loaded in shear wants shank in the shear plane, not thread — thread in the shear plane reduces the effective cross-section and puts the load on the root. Thread length also tells you whether a screw will bottom out in a blind hole before it clamps. Nominal length alone answers neither question, and a "fully threaded" boolean only answers it for the short end of the range.

Do I need to track hydrogen embrittlement relief on plated socket head cap screws?

For alloy steel, yes. ASTM F1941 is the coating spec for inch threaded fasteners — it supersedes B633 for this use — and it requires baking for fasteners specified at 40 HRC and above, flagging risk above 39 HRC and for case-hardened parts. Alloy steel SHCS sits squarely in that band. B633's 2007 revision also lengthened the bake for Grade-BD cap screws from 4 hours to 10 hours at 190-220°C. Plain (oiled) alloy steel and stainless are not exposed the same way. If you sell zinc-plated 12.9 or A574 into anything safety-critical, the bake spec and lot record belong on the product, not buried in a cert folder.

Should I list DIN 912 or ISO 4762?

List ISO 4762 as the governed value and keep DIN 912 as a search synonym. ISO 4762 is the current international standard; DIN 912 was withdrawn in favor of DIN EN ISO 4762. Across M3-M64 the head dimensions, socket sizes, and thread tolerances are effectively the same, which is why suppliers label stock "DIN 912 / ISO 4762" without much thought. One real difference worth knowing: the older DIN 912 allowed a thread-to-head option, while ISO 4762 specifies an unthreaded shank on longer screws. Buyers will keep typing DIN 912 for years because that is what is printed on their drawings — drop the synonym and you drop the search.

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