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العربية Metric stud bolts and inch stud bolts may look similar, but they are not interchangeable. The difference is not only the measuring unit. Thread form, pitch, nut fit, material standard, flange standard, torque practice, and certificate requirements can all change.
For buyers sourcing stud bolts for flanges, pressure piping, machinery, valves, pumps, or structural assemblies, the safest rule is simple: match the stud bolt system to the equipment standard. Do not convert by diameter only.
For standard and project-based supply, buyers can review XZ Fastener’s standard fasteners and threaded rod categories.
What Is a Metric Stud Bolt?
Defined by millimeters and metric thread pitch
Metric stud bolts are specified by nominal diameter and pitch in millimeters. A common callout may be M20 × 2.5 × 150 mm, meaning 20 mm nominal diameter, 2.5 mm pitch, and 150 mm length.
Metric stud bolts are common in ISO, DIN, EN, JIS, and many international machinery or construction projects.
| Metric Item | Example | Buyer’s Note |
|---|---|---|
| Diameter | M16, M20, M24 | Nominal size in millimeters |
| Pitch | 2.0, 2.5, 3.0 mm | Must match the nut |
| Length | 100 mm, 150 mm, 300 mm | Measured in millimeters |
| Nut type | DIN / ISO hex or heavy hex | Must match grade and thread |
| Common use | Machinery, equipment, global projects | Check DIN / ISO / project standard |
What Is an Inch Stud Bolt?
Defined by inches and threads per inch
Inch stud bolts are specified by nominal diameter, thread count, and length in inches. A common callout may be 3/4”-10 UNC × 6”, meaning 3/4 inch diameter, 10 threads per inch, coarse thread, and 6 inch length.
Inch stud bolts are widely used in ASTM, ASME, ANSI, oil and gas, flange, valve, and pressure equipment applications.
| Inch Item | Example | Buyer’s Note |
|---|---|---|
| Diameter | 1/2”, 3/4”, 1” | Nominal size in inches |
| Thread | UNC, UNF, 8UN | Must match nut and flange spec |
| Length | 4”, 6”, 12” | Measured in inches |
| Nut type | Heavy hex nut | Common in flange bolting |
| Common use | ASME flanges, piping, oil and gas | Check ASTM / ASME requirement |
Metric vs Inch Stud Bolts
Key differences buyers must confirm
| Selection Point | Metric Stud Bolts | Inch Stud Bolts |
|---|---|---|
| Unit system | Millimeters | Inches |
| Thread callout | Diameter × pitch | Diameter × TPI |
| Common standards | DIN, ISO, EN, JIS | ASTM, ASME, ANSI |
| Nut matching | Metric thread nut | UNC, UNF, or 8UN nut |
| Torque tables | Metric-based | Inch-based |
| Common certificates | MTC, EN 10204 3.1 if required | MTC, ASTM compliance if required |
| Typical market | Global machinery and construction | Oil, gas, piping, and U.S.-based projects |
The most common mistake is replacing an inch stud bolt with a “close” metric size. For example, M20 is not the same as 3/4”. The diameter, thread pitch, nut fit, and flange hole clearance may not match.
Material and Grade Requirements
Standards control more than size
Stud bolts are often ordered by material grade. Common examples include carbon steel, alloy steel, stainless steel, ASTM A193 B7, ASTM A320 L7, ASTM A193 B8, or metric property classes.
For material comparison, see XZ Fastener’s carbon steel fasteners and stainless steel fasteners.
RFQ Checklist for Buyers
Send the full specification
A clear RFQ should include:
- Metric or inch system.
- Diameter, pitch or TPI, and length.
- Thread standard and tolerance.
- Material grade and heat treatment requirement.
- Nut and washer requirement.
- Surface finish or coating.
- Certificate requirement.
- Application standard, such as flange, valve, pump, or machinery drawing.
For custom lengths, coatings, or project-specific certificates, send drawings and requirements through XZ Fastener Contact Us.
Final Recommendation
Choose metric stud bolts when the equipment, drawing, or project standard uses metric dimensions. Choose inch stud bolts when the flange, piping, valve, or project specification is based on ASTM, ASME, ANSI, UNC, UNF, or 8UN requirements.
Do not convert stud bolts by approximate size. Match the thread system, material grade, nut standard, coating, certificate, and application standard before ordering.