Fastener Guide / Head markings

Bolt Head Markings Chart

Identify a bolt by what is stamped on its head. Radial lines mean an SAE inch grade, numbers mean a metric property class, and letters mean an ASTM specification or a stainless class. The maker’s ID is not the grade.

Last reviewed 2026-09-11 · Governing standards: SAE J429, SAE J995, ASTM F3125, A307, A354, A449, A193, A194, A320, A563, F1554, F593, ISO 898-1, ISO 898-2, ISO 3506-1 · Report an error

Counter rule for SAE inch bolts: count the radial lines and add 2. Three lines = Grade 5, six lines = Grade 8. It fails in three places: a blank head is not proof of Grade 2; three lines can also be ASTM A449; and it never applies to metric numbers, ASTM letters or stainless. Letters or a logo off to the side are the manufacturer ID, not the grade.

Inch — SAE J429

MFG

SAE J429 Grade 2

No grade mark — maker ID only

Tensile 74 ksi min (1/4–3/4 in), 60 ksi (over 3/4 to 1-1/2 in)

Nut: SAE J995 Grade 2

A blank head is not proof of Grade 2. It can also be an unmarked unknown.

SAE J429

MFG

SAE J429 Grade 5

3 radial lines, 120° apart

Tensile 120 ksi min (1/4–1 in), 105 ksi (over 1 to 1-1/2 in)

Nut: SAE J995 Grade 5

The same three-line mark is used on ASTM A449 Type 1. Read the maker ID and the paperwork when it matters.

SAE J429

MFG

SAE J429 Grade 8

6 radial lines, 60° apart

Tensile 150 ksi min (1/4–1-1/2 in)

Nut: SAE J995 Grade 8

Close to metric 10.9 in strength but not interchangeable — different thread system and dimensions.

SAE J429

ASTM bolts, studs and anchor rods

307AMFG

ASTM A307 Grade A

307A when marked (often maker ID only)

Tensile 60 ksi min

Nut: ASTM A563 Grade A

General construction. Many A307 parts carry the maker ID only.

ASTM A307

MFG

ASTM A449 Type 1

3 radial lines and/or A449

Tensile 120 / 105 / 90 ksi by size

Nut: As specified (A563)

Looks like SAE Grade 5 on the head. Sizes and applications differ.

ASTM A449

BCMFG

ASTM A354 Grade BC

BC

Tensile 125 ksi min (to 2-1/2 in)

Nut: As specified (A563)

Alloy bolting and anchor applications.

ASTM A354

BDMFG

ASTM A354 Grade BD

BD

Tensile 150 ksi min (to 2-1/2 in)

Nut: ASTM A563 DH

Heavy industrial bolting.

ASTM A354

A325MFG

ASTM F3125 Grade A325

A325 on a heavy hex head

Tensile 120 ksi min

Nut: ASTM A563 (DH when galvanized)

Structural. Installed to RCSC methods, not a generic torque chart.

ASTM F3125

A325MFG

A325 Type 3 (weathering)

A325 underlined

Tensile 120 ksi min

Nut: ASTM A563 C3 / DH3

The underline identifies Type 3 weathering steel.

ASTM F3125

A490MFG

ASTM F3125 Grade A490

A490 on a heavy hex head (underlined = Type 3)

Tensile 150–173 ksi

Nut: ASTM A563 DH

Not plated or hot-dip galvanized. RCSC installation only.

ASTM F3125

B7

ASTM A193 Grade B7 stud

B7 on the stud end

Tensile 125 ksi min (to 2-1/2 in)

Nut: ASTM A194 2H

Flange, pressure and high-temperature bolting.

ASTM A193

L7

ASTM A320 Grade L7 stud

L7 on the stud end

Tensile 125 ksi min (to 2-1/2 in)

Nut: As specified for low-temperature service

Cold-service bolting.

ASTM A320

ASTM F1554 Grade 36

End painted blue

Tensile 58 ksi min

Nut: As specified (A563)

Anchor rods are identified by end color.

ASTM F1554

ASTM F1554 Grade 55

End painted yellow

Tensile 75 ksi min

Nut: As specified (A563)

Anchor rods are identified by end color.

ASTM F1554

ASTM F1554 Grade 105

End painted red

Tensile 125 ksi min

Nut: As specified (A563 DH)

Anchor rods are identified by end color.

ASTM F1554

Metric — ISO 898-1

4.6MFG

Property class 4.6

4.6

Tensile 400 MPa min

Nut: Class 5

Low strength. Marking is only required from class 8.8 up.

ISO 898-1

8.8MFG

Property class 8.8

8.8

Tensile 800 MPa (to M16) / 830 MPa (over M16)

Nut: Class 8

The most common metric structural-strength class.

ISO 898-1

9.8MFG

Property class 9.8

9.8

Tensile 900 MPa min (to M16)

Nut: Class 9

Only made up to M16.

ISO 898-1

10.9MFG

Property class 10.9

10.9

Tensile 1040 MPa min

Nut: Class 10

High strength. Electroplating needs a controlled, baked process.

ISO 898-1

12.9MFG

Property class 12.9

12.9 (usually a socket head)

Tensile 1220 MPa min

Nut: Class 12

Most often seen on socket head cap screws.

ISO 898-1

Stainless

18-8MFG

18-8 stainless

18-8 (or no mark)

Not a strength grade

Nut: Stainless, matched alloy

18-8 covers 302 / 303 / 304 / 305. A magnet is not a reliable alloy test.

Alloy family name

A2-70MFG

ISO 3506 A2-70

A2-70

Tensile 700 MPa min

Nut: A2-70

A2 = 304-type austenitic, cold worked.

ISO 3506-1

A4-80MFG

ISO 3506 A4-80

A4-80

Tensile 800 MPa min

Nut: A4-80

A4 = 316-type, strain hardened. Better in chlorides.

ISO 3506-1

F593CMFG

ASTM F593 Group 1 CW1

F593C

100 ksi min (1/4–5/8 in, CW1)

Nut: ASTM F594

C / D = 304 family CW1 / CW2; G / H = 316 family.

ASTM F593

Nuts

DH

ASTM A563 Grade DH nut

DH

Heavy hex, hardened

Nut: Pairs with A325 galvanized, A490, A354 BD

Heavy hex is a shape, not a grade.

ASTM A563

2H

ASTM A194 Grade 2H nut

2H

Heavy hex

Nut: Pairs with A193 B7

2HM pairs with B7M; 8 / 8M with B8 / B8M.

ASTM A194

10

ISO 898-2 class 10 nut

8 / 10 / 12

Metric nut class

Nut: Class 8 with 8.8, 10 with 10.9, 12 with 12.9

A weaker nut on a stronger bolt strips first.

ISO 898-2

Drawings show the mark, not the exact layout on every part. The maker’s ID position and style vary by manufacturer. A grade mark with no maker ID is incomplete and suspect.

Reference only. Markings identify the material grade the maker claims. For critical joints confirm with certifications and the governing standard. The drawing and the engineer govern.

Related sheets

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Mayport Tool & Die Inc.13.53.1
Eagle Mechanical LLC12.52.9
Premier Electric Group10.22.4
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Coastal Maintenance Group5.71.3
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