The everyday carbon-steel bolt standard — general-purpose fasteners where high clamp load isn't the priority.
ASTM A307 covers carbon-steel bolts and studs from 1/4″ through 4″ in diameter — the run-of-the-mill, general-purpose bolt specification, often manufactured from A36 round bar. It's the baseline grade specified where a connection doesn't demand the higher clamp loads of a heat-treated fastener.
The standard is issued in three grades — A, B, and C — that differ by tensile strength, configuration, and intended application. The mechanical differences between them are relatively small.
A307 heads carry the manufacturer's identification symbol and the grade marking — “307A” or “307B” for the corresponding grade. Because A307 is a plain carbon-steel grade, it does not use the SAE radial-line system reserved for heat-treated J429 grades.
| Grade | Typical Use |
|---|---|
| Grade A | Headed bolts, threaded rods, and bent bolts for general applications. |
| Grade B | Heavy hex bolts and studs for flanged joints in piping systems with cast-iron flanges. |
| Grade C | Nonheaded anchor bolts, bent or straight, for structural anchorage. Superseded — see note below. |
As of August 2007, A307 Grade C was replaced by ASTM F1554 Grade 36. Many suppliers will still furnish Grade C when a project specifically requires it.
| Grade | Size Range | Tensile | Yield, min | Elongation, min |
|---|---|---|---|---|
| Grade A | 1/4″ thru 4″ | 60,000 psi min | — | 18% |
| Grade B | 1/4″ thru 4″ | 60,000–100,000 psi | — | 18% |
| Grade C | 1/4″ thru 4″ | 58,000–80,000 psi | 36,000 psi | 23% |
Grade B carries a tensile range (a ceiling as well as a floor) because it mates with cast-iron flanges — too much strength is as undesirable as too little. Grades A and B have no specified yield.
| Element | Grade A, max | Grade B, max |
|---|---|---|
| Carbon | 0.29% | 0.29% |
| Manganese | 1.20% | 1.20% |
| Phosphorus | 0.04% | 0.04% |
| Sulfur | 0.15% | 0.05% |
| Bolt Grade | Size | Nut |
|---|---|---|
| Grades A & C | 1/4″ – 1-1/2″ | ASTM A563 Grade A hex |
| Grades A & C | 1-5/8″ – 4″ | ASTM A563 Grade A heavy hex |
| Grade B | 1/4″ – 4″ | ASTM A563 Grade A heavy hex |
Washers are unspecified for A307. In the SAE world, A307 is the usual equivalent to a Grade 2 fastener.