ASTM A193 B7 Stud Bolt with A194 2H Hex Nuts ASME B18.2.1 ASME B18.2.2
ASTM A193 Grade B7 stud bolts with ASTM A194 Grade 2H hex nuts are widely used for flange bolting in high-pressure and elevated-temperature piping systems. A typical flange bolting set consists of one fully threaded B7 stud bolt and two A194 2H heavy hex nuts, with one nut installed on each end of the stud.
These products are frequently searched or specified commercially as “ASME B18.2.1 Stud Bolt & ASME B18.2.2 Hex Nuts.” Technically, ASME B18.2.1 applies primarily to headed bolts and screws, while ASME B18.31.2 is the more specific dimensional standard for continuous-thread and flange bolting studs. ASME B18.2.2 covers hex and heavy hex nuts.
ASME B18.2.1 Stud Bolt & ASME B18.2.2 Hex Nuts
The phrase “ASME B18.2.1 Stud Bolt” is commonly used in purchasing enquiries, drawings and online searches for flange bolting.
For technical specification purposes, the standards are better separated as follows:
| Item | Applicable Standard |
|---|---|
| Stud Bolt Material | ASTM A193 Grade B7 |
| Nut Material | ASTM A194 Grade 2H |
| Flange Stud Dimensions | ASME B18.31.2 |
| Hex / Heavy Hex Nut Dimensions | ASME B18.2.2 |
| Thread Form | ASME B1.1 as applicable |
| Flange Application | ASME B16.5 / ASME B16.47 |
ASME B18.2.1 remains an important search and purchasing term, but for fully threaded flange studs, ASME B18.31.2 gives the more specific stud dimensional requirements.
ASTM A193 B7 / A194 2H Specification
| Item | Specification |
|---|---|
| Stud Bolt Grade | ASTM A193 / A193M B7 |
| Nut Grade | ASTM A194 / A194M 2H |
| Typical Assembly | 1 Stud + 2 Nuts |
| Stud Type | Fully Threaded / Flange Bolting Stud |
| Stud Standard | ASME B18.31.2 |
| Nut Standard | ASME B18.2.2 |
| Stud Material | Cr-Mo Alloy Steel |
| Nut Material | Heat-Treated Carbon Steel |
| Heat Treatment | Quenched & Tempered |
| Typical Application | Flanges, Valves, Fittings, Pressure Equipment |
| Coating Options | Plain / Zinc / HDG / Zinc-Nickel / PTFE |
What Is ASTM A193 Grade B7?
ASTM A193 Grade B7 is a chromium-molybdenum alloy-steel bolting grade used for high-pressure, elevated-temperature and other pressure-system applications.
B7 bolting is widely used for:
- Pipe flanges
- Valves
- Pressure vessels
- Pipe fittings
- Petrochemical equipment
- Refinery piping
- Power-generation systems
B7 is commonly manufactured from 4140/4142-type Cr-Mo alloy steel chemistry and is quenched and tempered to achieve the required strength.
The grade designation is ASTM A193 B7; it should not simply be described as AISI 4140 because ASTM material requirements include their own chemistry, heat treatment and mechanical-property criteria.
What Is ASTM A194 Grade 2H?
ASTM A194 Grade 2H is a heat-treated carbon-steel nut grade commonly used with ASTM A193 B7 stud bolts.
For flange bolting, the nut is typically supplied in heavy hex form according to ASME B18.2.2 dimensions.
The common B7/2H bolting combination provides:
- High-strength flange clamping
- Compatibility with pressure piping applications
- Reliable bolted-joint performance
- Wide availability in multiple diameters and coatings
Why Does One B7 Stud Use Two A194 2H Nuts?
A fully threaded flange stud has no integral bolt head.
The stud passes through the bolt holes of two mating flanges and is tightened from both sides.
Therefore, a typical flange bolting set contains:
1 × ASTM A193 B7 Stud Bolt
2 × ASTM A194 Grade 2H Nuts
This is one of the most common bolting configurations for ASME pressure-piping flange joints.
ASTM A193 B7 Chemical Composition
| Element | ASTM A193 B7 |
|---|---|
| Carbon, C | 0.37–0.49% |
| Manganese, Mn | 0.65–1.10% |
| Phosphorus, P | 0.035% max |
| Sulfur, S | 0.040% max |
| Silicon, Si | 0.15–0.35% |
| Chromium, Cr | 0.75–1.20% |
| Molybdenum, Mo | 0.15–0.25% |
The chromium-molybdenum composition supports the strength and elevated-temperature performance required for pressure bolting.
Actual heat chemistry should be confirmed by the supplied material certificate.
ASTM A193 B7 Mechanical Properties
B7 strength requirements vary with nominal stud diameter.
| Nominal Diameter | Tensile Strength Min. | Yield Strength Min. | Elongation Min. | Reduction of Area Min. |
|---|---|---|---|---|
| Up to 2-1/2 in. | 125 ksi | 105 ksi | 16% | 50% |
| 2-5/8–4 in. | 115 ksi | 95 ksi | 16% | 50% |
| 4-1/8–7 in. | 100 ksi | 75 ksi | 18% | 50% |
The mechanical properties should therefore be selected according to actual stud diameter rather than presenting one universal strength value.
Stud Bolt Dimensions and Threads
For flange bolting studs, the purchase specification should normally define:
- Stud diameter
- Overall stud length
- Thread pitch
- Thread series
- Thread class when specified
- Nut size
- Coating
- Quantity
Unified inch threads may follow ASME B1.1 as applicable.
Stud length should be determined from the actual flange type, pressure class, gasket configuration and required nut engagement.
For standard flange joints, dimensions should not be selected only from nominal pipe size.
ASME B18.31.2 vs ASME B18.2.1
This distinction is important for both technical accuracy and purchasing.
ASME B18.2.1
ASME B18.2.1 primarily covers inch-series:
- Square bolts
- Hex bolts
- Heavy hex bolts
- Related headed screws
It is therefore not the most specific standard for continuous-thread flange studs.
ASME B18.31.2
ASME B18.31.2 specifically addresses:
- Continuous-thread studs
- Double-end studs
- Flange bolting studs
For a fully threaded flange stud, ASME B18.31.2 is the more appropriate dimensional reference.
ASME B18.2.2
ASME B18.2.2 covers inch-series nuts, including:
- Hex nuts
- Heavy hex nuts
- Square nuts
- Other related nut forms
ASTM A194 Grade 2H heavy hex nuts are therefore commonly supplied to ASME B18.2.2 dimensions.
Surface Coatings for B7 Stud Bolts
ASTM A193 B7 stud bolts can be supplied with different surface treatments according to corrosion exposure, installation conditions and project requirements.
| Coating | Typical Use |
|---|---|
| Plain / Black | General industrial service |
| Zinc Plating | Basic corrosion protection |
| Hot-Dip Galvanized | Outdoor or corrosive environments |
| Zinc-Nickel | Enhanced corrosion resistance |
| PTFE / Fluoropolymer | Corrosion protection and controlled friction |
| Cadmium | Special applications where legally permitted |
PTFE / Fluoropolymer Coated Stud Bolts
PTFE or fluoropolymer coating systems are commonly used for flange bolting where corrosion protection and controlled friction are required.
Systems such as Xylan®-type coatings may be supplied when specified.
Because coating changes the coefficient of friction, it can significantly affect the relationship between applied torque and actual bolt tension.
For coated bolting, installation torque should therefore follow the approved project bolting procedure and coating-specific friction data.
Are Washers Required with B7 Stud Bolts?
Not in every flange joint.
A standard bolting set is commonly supplied as:
1 B7 Stud Bolt + 2 A194 2H Nuts
Washers may be added if required by the project specification, piping standard or bolting procedure.
ASTM F436 hardened washers may be used in certain bolting applications, but they should not be described as mandatory for every ASME flange connection.
Typical B7 / 2H Flange Bolting System
A common carbon-steel pressure piping system may use:
| Component | Typical Specification |
|---|---|
| Flange | ASTM A105 |
| Stud Bolt | ASTM A193 B7 |
| Heavy Hex Nut | ASTM A194 2H |
| Flange Dimensions | ASME B16.5 |
| Stud Dimensions | ASME B18.31.2 |
| Nut Dimensions | ASME B18.2.2 |
For many carbon-steel pressure piping systems, ASTM A105 flanges are commonly assembled using ASTM A193 B7 stud bolts and ASTM A194 2H heavy hex nuts, subject to the piping class and project bolting specification.
This creates a useful internal product relationship:
ASTM A105 Flange → ASTM A193 B7 Stud Bolt → ASTM A194 2H Nut
ASTM A193 B7 vs ASTM A320 L7
ASTM A193 B7 and ASTM A320 L7 are both high-strength alloy-steel bolting grades, but their primary service focus differs.
| Item | ASTM A193 B7 | ASTM A320 L7 |
|---|---|---|
| Primary Service | High pressure / elevated temperature | Low-temperature service |
| Material Family | Cr-Mo alloy steel | Cr-Mo alloy steel |
| Low-Temp Toughness | Not the primary grade basis | Low-temperature testing required |
| Common Flange Pairing | ASTM A105 | ASTM A350 LF2 |
| Common Nut | ASTM A194 2H | ASTM A194 Grade 7 as applicable |
For low-temperature carbon-steel piping systems, a common material relationship is:
ASTM A350 LF2 Flange → ASTM A320 L7 Stud Bolt → ASTM A194 Grade 7 Nut
The applicable bolting combination must still follow the project piping specification.
Inspection & Certification
ASTM A193 B7 stud bolts and A194 2H nuts can be supplied with:
- Material Test Certificate
- Chemical composition results
- Mechanical-property test results
- Hardness testing
- Dimensional inspection
- Thread inspection
- Coating inspection
- Visual inspection
- Heat / lot traceability
- Third-party inspection when required
EN 10204 Type 3.1 documentation may be supplied when agreed in the purchase specification.
Frequently Asked Questions
What is ASTM A193 B7 stud bolt?
ASTM A193 B7 is a quenched-and-tempered chromium-molybdenum alloy-steel bolting grade used for flange joints, valves, pressure vessels and other high-pressure or elevated-temperature applications.
What nut is used with ASTM A193 B7?
ASTM A194 Grade 2H heavy hex nuts are one of the most common nut grades used with ASTM A193 B7 stud bolts.
A typical flange set contains one B7 stud and two 2H nuts.
Does ASME B18.2.1 cover stud bolts?
Not specifically. ASME B18.2.1 primarily covers headed bolts and screws. For continuous-thread and flange bolting studs, ASME B18.31.2 is the more specific dimensional standard.
What standard covers A194 2H hex nuts?
ASME B18.2.2 covers inch-series hex and heavy hex nut dimensions. ASTM A194 defines the material and mechanical requirements for Grade 2H nuts.
What is the difference between B7 and L7 stud bolts?
B7 is primarily used for high-pressure and elevated-temperature bolting, while A320 L7 is intended for low-temperature bolting service and includes low-temperature toughness requirements.
ASTM A193 B7 Stud Bolt Manufacturer
We manufacture and supply ASTM A193 B7 fully threaded stud bolts with ASTM A194 Grade 2H heavy hex nuts for oil & gas, petrochemical, refinery, power and industrial pressure-piping projects.
Available options include:
Plain, zinc-plated, hot-dip galvanized, zinc-nickel and PTFE / fluoropolymer-coated stud bolts, with custom diameters, lengths and thread requirements.
For quotation, please specify:
Stud Grade + Nut Grade + Diameter + Length + Thread + Coating + Quantity + Required Standard
Example:
ASTM A193 B7 Stud Bolt, 1-1/4″-8UN × 300 mm, with 2 × ASTM A194 2H Heavy Hex Nuts, PTFE Coated
