A307 and A193 bolts can look identical on a job site. Same hex profile, same thread form, sometimes the same diameter. But the physical resemblance is where the similarity ends. These two standards cover fundamentally different materials, mechanical properties, and intended service environments. One is a low-carbon steel fastener designed for general and light structural use. The other is an alloy or stainless steel bolting specification built for high-temperature, high-pressure, and pressure-retaining service where joint integrity is a code requirement, not just a preference.
The grade confusion between them costs real money, either in over-specification when A307 would have been sufficient, or in system failures and failed inspections when A307 is used where ASTM A193 bolts are required. Knowing what separates these two standards at the material, mechanical, and application level removes that ambiguity from the procurement process.
What the Grade Designation Actually Tells You
ASTM designations on fasteners are not brand names or quality tiers. They are material and performance specifications published by ASTM International that define exactly what a fastener is made of, how it was processed, and what mechanical properties it must meet. When a bolt is marked A307 or A193, that marking is a claim about chemical composition, heat treatment, minimum tensile and yield strength, and the service conditions the fastener was designed to handle.
A307 and A193 sit at opposite ends of the industrial bolt spectrum. A307 is a low-carbon steel specification requiring a minimum tensile strength of 60 ksi, with no heat treatment required and no yield strength minimum in most grades. A193 is a high-temperature service specification covering alloy steel and stainless steel bolting with minimum tensile strengths up to 125 ksi for the most common grades, achieved through defined heat treatment processes. The mechanical gap between them is not minor. It determines whether a bolted joint remains intact under elevated temperature, cyclic loading, and the internal stresses of pressurized service.
ASTM A307 Grades A, B, and C in Industrial Use
The ASTM A307 specification covers carbon steel bolts and studs in diameters from 1/4 inch through 4 inches. The standard defines three grades, each with a distinct application scope.
Grade A covers general-purpose carbon steel bolts with a minimum tensile strength of 60 ksi and no minimum yield strength requirement. These are the most widely used A307 fasteners in light structural work, non-critical mechanical assemblies, and construction applications where load demands are modest and the service environment is ambient temperature. Grade A bolts carry no head markings indicating grade, which makes field identification reliant on documentation and purchase order traceability.
Grade B covers heavy hex bolts and fully threaded studs specifically designed for use in cast iron flanged connections, particularly in water and steam distribution systems where the mating flange material is cast iron rather than carbon steel. Grade B carries the same 60 ksi minimum tensile requirement as Grade A but is dimensionally configured for the heavy hex bolt pattern that cast iron flanged joints require. It is not a substitute for A193 stud bolts in ASME B16.5 carbon steel flanged connections.
Grade C, originally covering anchor bolts, was withdrawn in 2007 and replaced by ASTM F1554 Grade 36. Grade C products can still be manufactured to order if specified, but F1554 is now the current standard for anchor bolt applications. Procurement teams sourcing anchor bolts should verify the governing specification on the drawing before ordering against the older grade designation.
ASTM A193 Grades Across Alloy and Stainless Steel
The ASTM A193 specification covers alloy and stainless steel bolting materials for use in high-temperature and high-pressure service. The standard is organized around grade designations that identify both the base material and, in some cases, the heat treatment class. The most widely specified grades in industrial piping and process equipment are B7, B8, and B8M.
Grade B7 is a chromium-molybdenum alloy steel stud bolt produced in the quenched and tempered condition. For diameters up to 2.5 inches, ASTM A193 B7 stud bolts carry a minimum tensile strength of 125 ksi and a minimum yield strength of 105 ksi. These properties are achieved through controlled heat treatment, not merely through alloy composition. B7 is the standard bolting grade for carbon steel flanged piping systems covered under ASME B16.5 and ASME B31.3, and it is routinely specified for service from -40°F through 1000°F depending on the governing code and system design.
Grade B8 covers austenitic stainless steel bolting manufactured from Type 304 stainless steel. Class 1 B8 bolts are solution annealed and carry a minimum tensile strength of 75 ksi. Class 2 B8 bolts are strain hardened to a minimum tensile strength of 125 ksi, making them suitable for higher-load stainless applications. Grade B8M covers the same class structure but uses Type 316 stainless steel, which provides better resistance to chloride-containing environments. B8 and B8M are specified in systems where galvanic compatibility with stainless steel flanges or fittings is required, and in corrosive service applications where carbon steel bolting would degrade.
Mechanical Properties Side by Side
The table below compares the key mechanical properties across the most commonly specified grades under both standards. Values shown are for standard diameter ranges; larger diameters within A193 carry reduced requirements as defined in the specification.
| Property | A307 Grade A | A307 Grade B | A193 B7 | A193 B8 Cl.1 | A193 B8 Cl.2 |
| Base Material | Low-carbon steel | Low-carbon steel | Cr-Mo alloy steel | 304 stainless | 304 stainless |
| Min. Tensile Strength | 60 ksi | 60 ksi | 125 ksi (≤2.5″) | 75 ksi | 125 ksi |
| Min. Yield Strength | Not specified | Not specified | 105 ksi (≤2.5″) | 30 ksi | 100 ksi |
| Heat Treatment | None required | None required | Quenched and tempered | Solution annealed | Strain hardened |
| Typical Nut Pairing | A563 Grade A | A563 Grade A heavy hex | A194 Grade 2H | A194 Grade 8 | A194 Grade 8 |
| Primary Application | General structural, light assembly | Cast iron flanged connections | Steel pressure flanges, high-temp service | Corrosion-resistant service | High-load corrosion-resistant service |
The absence of a yield strength requirement in A307 is a significant distinction. In a joint under sustained load or thermal cycling, yield strength governs how much the fastener can stretch elastically before taking a permanent set. A fastener with no minimum yield requirement provides no predictable reserve between working load and permanent deformation, which is why A307 is restricted to applications where load conditions are static, modest, and ambient temperature.
Temperature and Pressure Service Limits
Temperature is one of the clearest dividing lines between A307 and A193 applications. A307 low-carbon steel bolts are not covered by ASME B16.5 pressure-temperature rating tables, which means they are not recognized for use in code-governed flanged piping systems. In practice, A307 bolts are considered acceptable for ambient-temperature utility service with cast iron flanges per A307 Grade B, but they are not suitable for steam service, high-pressure process piping, or any application where the joint is governed by a pressure piping code.
A193 B7 alloy steel stud bolts are listed in ASME B16.5 and maintain their rated mechanical properties across a service range from -40°F to 1000°F at the upper bound of code-governed service. The quench-and-temper heat treatment that achieves B7’s 125 ksi tensile strength is also what preserves that strength at elevated temperature, unlike low-carbon steel, which loses strength progressively as temperature rises and has no defined lower limit for acceptable performance at elevated conditions.
For flanged pipe systems, including those on refinery process lines, upstream production separators, gas processing equipment, and heat exchanger nozzles, A193 B7 stud bolts paired with A194 Grade 2H heavy hex nuts are the code-required bolting assembly. Substituting A307 bolts in those applications is a code violation, not a cost-saving option. The combination of flanges and matched bolting to the correct ASTM grade is what the pressure-temperature rating of the joint depends on.
When A307 Works and When A193 Is Required
A307 Grade A is appropriate for structural connections, equipment mounting, non-pressure mechanical assemblies, and applications where the governing standard does not specify a higher bolt grade. Buildings, bridges, conveyor frames, non-pressurized tank structures, and general industrial construction commonly use A307 Grade A or comparable low-carbon fasteners where load conditions are within the 60 ksi tensile capacity and temperature is ambient. The cost advantage over A193 is real, and in these applications there is no technical reason to spend more.
A307 Grade B has a narrower scope. It is specifically intended for bolted joints in cast iron flanges, including water mains, fire protection piping, and low-pressure utility distribution systems where the fitting material is cast iron and the service conditions do not require the higher strength and temperature capacity of A193. Using A193 B7 in a cast iron flange water main is not harmful, but it is unnecessary and significantly more expensive.
A193 is required wherever the joint is governed by a pressure piping code that specifies it, wherever elevated temperature is part of the service envelope, or wherever the design basis of the joint was developed using the mechanical properties of A193 grades. This includes ASME B16.5 flanged connections in carbon steel and stainless steel systems, ASME B31.3 process piping, ASME pressure vessel connections, and any application where the engineer of record has specified A193 on the drawing. In those cases, the specification is not a suggestion. It is the basis for the joint’s rated load capacity.
Industrial Bolt Grades Stocked and Ready to Ship
Coastal Resources Group stocks and supplies industrial fasteners across both standards, serving petrochemical, refinery, oilfield, water treatment, construction, and heavy industrial operations throughout Texas and beyond. Orders are filled against the specification, with full grade traceability from purchase order through delivery.
What Coastal supplies across A307 and A193 applications:
- ASTM A193 B7 and B8 stud bolts with matching A194 nut grades in standard and custom lengths across all ASME B16.5 flange classes
- B8 and B8M stainless stud bolts in Class 1 and Class 2 configurations for corrosion-resistant and high-purity service
- A307 Grade A and Grade B hex bolts and fully threaded studs in standard diameters for structural and cast iron flange applications
- Full bolting packages paired with industrial flanges and gaskets for single-supplier procurement on piping and vessel projects
- Specialty and high-alloy grades for sour service, cryogenic, marine, and high-temperature applications beyond standard A193 coverage
- 24/7 sales availability with same-day fulfillment options for field requisitions and emergency supply needs
Contact us to request a quote on A307 or A193 fasteners matched to the service conditions and code requirements of the application.