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ASTM & ISO Fastener Grade Markings | Aanuraj

ASTM & ISO Fastener Grade Markings

Compact identification guide for bolts, studs and nuts — with current-standard notes and clean marking examples.

1. How Fastener Markings Work

A fastener marking normally identifies the applicable grade/property class and, where required by the product specification, the manufacturer's identification. The marking is not a substitute for the purchase specification or material test certificate.

ASTM A193B7
Example: alloy/stainless bolting grade
ASTM A193B8M
Example: 316-type austenitic grade
ISO 898-18.8
Carbon/alloy steel property class
ISO 3506-1A4-80
Stainless-steel grade + property class

2. ASTM — Bolts & Studs

The original Aanuraj page contains a broad historical identification table. The compact table below keeps the principal grades relevant to the site's fastener business and removes the damaged grade-mark images.

MarkingSpecificationTypical material / grade familyFastener
B7ASTM A193/A193MCr-Mo alloy steel; AISI 4140/4142/4105 material family is shown on the Aanuraj reference.Bolts, studs, stud bolts
B16ASTM A193/A193MCr-Mo-Va alloy steelBolts, studs
B8ASTM A193/A193M304-type austenitic stainless steelBolts, studs
B8MASTM A193/A193M316-type austenitic stainless steelBolts, studs
B8CASTM A193/A193M347-type austenitic stainless steelBolts, studs
B8TASTM A193/A193M321-type austenitic stainless steelBolts, studs
L7ASTM A320/A320MAlloy steel for low-temperature serviceBolts, studs
Marking principle: ASTM A193 requires grade/class and manufacturer identification in the locations specified by the standard. For example, B7 is the grade symbol; it is not a generic “high tensile” marking.

3. ISO 898-1 — Carbon & Alloy Steel

The old Aanuraj page uses “ISO R898”. For a current technical page, use ISO 898-1:2013, which ISO says remains current after its 2025 review. citeturn0search2

Property classMeaningTypical useMaterial family
4.6ISO property classGeneral-purpose metric fastenersCarbon / alloy steel
5.8ISO property classGeneral engineering fastenersCarbon / alloy steel
8.8ISO property classHigh-strength engineering fastenersCarbon / alloy steel
10.9ISO property classHigh-strength applicationsAlloy / carbon steel
12.9ISO property classVery high-strength applicationsAlloy steel
Do not mix systems: ISO 898-1 property classes are not direct equivalents of ASTM A193 grades such as B7. Select the grade/specification required by the application and purchase specification.

4. ISO 3506-1 — Stainless Steel Fasteners

For stainless bolts, screws and studs, the relevant current standard is ISO 3506-1:2020. ISO confirms this edition was reviewed and confirmed in 2025. citeturn5search0

AusteniticA2-70
Common 304-type stainless fastener designation
AusteniticA4-70
Common 316-type stainless fastener designation
AusteniticA4-80
Higher property class within the A4 family
DuplexD*
Duplex grades use the ISO 3506 designation system; exact grade/class must be specified.
Important: A2/A4 designations are ISO stainless-fastener designations, not ASTM A193 B8/B8M designations. They should not be presented as identical standards.

5. ASTM — Nut Identification

The original Aanuraj page contains ASTM A563 and ASTM A194 nut markings. The key industrial grades are retained below without the damaged images.

Nut markingSpecificationMaterial / serviceTypical pairing / note
2HASTM A194/A194MMedium-carbon steel, quenched & temperedCommon companion nut for ASTM A193 B7 applications
2HMASTM A194/A194MAlloy/medium-carbon steel grade for specified serviceUse only where the purchase specification calls for it
8ASTM A194/A194M304-type stainlessUsed with applicable stainless bolting systems
8MASTM A194/A194M316-type stainlessUsed with applicable B8M-type bolting systems
8CASTM A194/A194M347-type stainlessUsed with applicable B8C-type bolting systems
8TASTM A194/A194M321-type stainlessUsed with applicable B8T-type bolting systems

ASTM A194/A194M is an active specification for carbon, alloy and stainless steel nuts for high-pressure and/or high-temperature service. ASTM lists A194/A194M-26 as active. citeturn3search5

6. Nickel & High-Nickel Alloy Grades

These are material-grade references commonly used for high-nickel fasteners. The ASTM references below are material/product specifications for the indicated forms; they are not automatically the complete fastener specification.

FamilyGradeUNSCommon ASTM material reference
Inconel600N06600ASTM B166 — rod, bar & wire
Inconel625N06625ASTM B446 — rod & bar; ASTM B564 — forgings
Inconel718N07718ASTM B637 — bar, forgings & forging stock
Inconel / Alloy 825825N08825ASTM B425 — rod & bar; ASTM B564 — forgings
Monel400N04400ASTM B164 — rod, bar & wire
MonelK-500N05500ASTM B865 — bar, rod, wire & forgings
Alloy 20Alloy 20N08020ASTM B473 — bar & wire
Specification note: For an actual bolt, nut or stud purchase, specify the complete fastener/product specification, grade, size, thread, heat treatment and required testing. The ASTM B-series references above identify material forms and are not by themselves a universal fastener standard.

7. Important Technical Corrections

  • ISO R898: replace the old “ISO R898” label with ISO 898-1:2013 for the current carbon/alloy-steel property-class reference. citeturn0search2
  • Stainless steel: use ISO 3506-1:2020 for current stainless bolts, screws and studs; it covers austenitic, martensitic, ferritic and duplex stainless fasteners. citeturn5search0
  • A325/A490: the old page presents these as standalone ASTM specifications. ASTM F3125/F3125M consolidated and replaced A325, A325M, A490, A490M, F1852 and F2280; current documents should therefore specify the applicable F3125 grade/type/style where required. citeturn3search2
  • Do not call every marking an “equivalent”. ASTM grades, ISO 898 property classes and ISO 3506 stainless designations are different specification systems.
  • Images removed: the old page's marking pictures were broken/externally hosted. This redesign uses clean HTML marking examples, so there are no external marking-image dependencies.
  • Inspection: final acceptance should be based on the applicable product standard, marking requirements, dimensions, MTC and purchase order—not the head/nut marking alone.

Buy Online & Technical Enquiry

For standard fasteners and online purchasing, visit NutsAndBoltsOnline. For grade, size, quantity, drawing or technical requirements, contact Aanuraj directly.

8. Source References

Aanuraj original marking page: aanuraj.com/astm-and-iso-grade-markings-on-fasteners
ISO 898-1:2013: ISO official reference citeturn0search2
ISO 3506-1:2020: ISO official reference citeturn5search0
ASTM F3125/F3125M: ASTM official reference citeturn3search2
ASTM A194/A194M: ASTM official reference citeturn3search5