Grades stocked: A · B
Scope
ASTM A307 covers carbon steel bolts, studs, and threaded rod in inch and metric sizes from 1/4" through 4" diameter, with a specified minimum tensile strength of 60,000 psi. It is the base-level, non-heat-treated bolt specification and the default callout for non-structural, non-critical, low-stress applications.
A307 is not a structural bolt. Where high-strength connections are required, specify F3125. Where elevated temperature or pressure is involved, specify A193. Where anchor service is required, specify F1554.
Grades
| Grade | Use | Head style |
|---|---|---|
| A | General applications; the default A307 callout | Square or hex head; any head style permitted |
| B | Cast-iron flanged joints in pressure piping, specifically to limit tensile strength ceiling to protect cast-iron flanges | Heavy hex head required |
Grade C historically existed as the anchor-bolt grade but was withdrawn from A307 in 2007. It was replaced by ASTM F1554 Grade 36. Old drawings citing "A307 Grade C" should be re-specified to F1554 Grade 36 on new work.
Mechanical properties
Grade A
- Tensile: 60 ksi minimum (no maximum)
- Yield: Not specified
- Elongation in 2": 18% minimum
- Reduction of area: 35% minimum
- Hardness: 69 HRB to 95 HRB (121–212 HBW)
Grade B
- Tensile: 60 ksi minimum, 100 ksi maximum (the ceiling protects cast-iron flanges from cracking)
- Yield: Not specified
- Elongation in 2": 18% minimum
- Reduction of area: 35% minimum
- Hardness: 69 HRB to 95 HRB
Chemistry
A307 is low-carbon steel with no required alloy content:
- Carbon: 0.30% max (Grade A); not specified (Grade B)
- Manganese, phosphorus, sulfur: standard commercial limits
- Not heat-treated; properties come from base composition and cold-finishing
Recommended nuts and washers
| Bolt | Nut | Washer |
|---|---|---|
| Grade A | A563 Grade A (hex or heavy hex) | F844 plain flat |
| Grade B | A563 Grade A or B (heavy hex) | F844 plain flat |
For applications where corrosion matters, move to stainless (F593) or coated (galvanized per F2329, zinc plated per F1941).
Applications
- General mechanical assembly
- Low-pressure flange bolting (Grade B with cast-iron flanges)
- Non-structural steel framing
- HVAC and plumbing support
- Equipment and machinery assembly
- Agricultural and industrial hardware
- Fence and railing
- Pipe hangers and supports
What A307 is NOT for
- Structural connections. Use F3125 for high-strength structural bolts.
- Anchor bolts. Use F1554 (Grades 36, 55, or 105 by load).
- Flange bolting on high-pressure / high-temperature service. Use A193.
- Low-temperature or cryogenic service. Use A320.
- Corrosive environments. Use stainless (F593) or specify coatings.
- Any application where bolt yield strength is a design input. A307 does not specify a yield.
Marking
- Grade A: no marking required (optional)
- Grade B: must be marked with "307B" or equivalent; heavy hex head required
- Manufacturer's identification symbol may appear on both
Related specifications
- F3125 — High-strength structural bolts (when A307 is not enough)
- F1554 — Anchor bolts (replaces old A307 Grade C)
- A563 — Nuts (Grade A pairs with A307)
- F844 — Plain flat washers
- F2329 — Hot-dip galvanizing
- F1941 — Zinc electroplating
Documentation
California Fastener A307 orders ship with mill certificates showing grade, heat number, chemistry, tensile, and hardness test results.