Fastener Guide / Technical Reference

ASTM A307 Grade B Bolts

A307 Grade B is the carbon-steel bolt written for flanged joints in piping systems with cast-iron flanges. Its tensile range is capped so the bolt cannot overload a brittle flange.

Last reviewed 2026-09-10 · Governing standard: ASTM A307-21; ASTM A563/A563M-26 · reference FG-60D944 · Report an error on this sheet

NutASTM A563 Grade A heavy hex
Why the max tensileProtects cast-iron flanges from over-tightening

Grade A vs Grade B

Grade AGrade B
Tensile60 ksi min60 - 100 ksi
HardnessB69 - B100B69 - B95
Typical headHex or heavy hexHeavy hex
UseGeneral constructionCast-iron flanged piping
Marking307A + maker (when marked)307B + maker (when marked)

These tables carry the same figures as the printed sheet below.

The printed sheet

ASTM A307 Grade B Bolts

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Text version of this sheet

ASTM A307 · Grade B · bolts for cast-iron flanged piping

What it is

FIELD IDENTIFICATION

A307 Grade B is the carbon-steel bolt written for flanged joints in piping systems with cast-iron flanges.

Its tensile range is capped so the bolt cannot overload a brittle flange.

MFG

307B

Nut

ASTM A563 Grade A heavy hex

Why the max tensile

Protects cast-iron flanges from over-tightening

Marked 307B + manufacturer ID (usually heavy

hex)

Grade A vs Grade B

Grade A

Grade B

Tensile

60 ksi min

60 - 100 ksi

Hardness

B69 - B100

B69 - B95

Typical head

Hex or heavy hex

Heavy hex

Use

General construction

Cast-iron flanged piping

Marking

307A + maker (when marked)

307B + maker (when marked)

Key points

Do not upgrade to a higher-strength bolt on cast-iron flanges without the piping engineer: a stronger bolt can crack the flange.

Governing standards: ASTM A307-21; ASTM A563/A563M-26. Editions shown are the latest confirmed as of September 2026. The drawing and the governing standard always take

precedence over this sheet.

torquing any fastener. Verify the current governing standard, project documents, OEM requirements, size, thread, coating and lot certification. To the fullest extent permitted by law, The Fastener App disclaims liability

arising from reliance on this reference.

Fastener Guide reference FG-60D944 · thefastenerapp.com/fastener-guide/technical-reference/astm-a307-grade-b-bolts · © The Fastener App. Reference only — verify the current governing standard, drawing and manufacturer data before specifying or installing.

Related sheets

← ASTM A307 Grade A BoltsASTM A354 Grade BC →

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