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العربية Imperial fasteners are still widely used in the United States, Canada, and many maintenance markets supplied by U.S.-standard equipment. For importers and distributors, the main challenge is not only stocking inch sizes. It is identifying the correct diameter, thread series, length, grade, and matching parts before placing the order.
A 1/2 inch bolt and an M12 bolt may look close, but they are not interchangeable. The thread system must be confirmed first.
What Imperial Fastener Sizes Mean
Imperial fasteners are usually specified by fractional diameter, thread count, and length. A common description looks like this:
1/2”-13 UNC × 2”
This means:
- 1/2 inch nominal diameter
- 13 threads per inch
- UNC coarse thread
- 2 inch overall length
For regular stock items, buyers can review standard fasteners and bolt products before preparing an RFQ.
Common Imperial Bolt Size Chart
| Nominal Size | Decimal Diameter | UNC Thread | UNF Thread |
|---|---|---|---|
| #6 | 0.138 in | 32 TPI | 40 TPI |
| #8 | 0.164 in | 32 TPI | 36 TPI |
| #10 | 0.190 in | 24 TPI | 32 TPI |
| 1/4” | 0.250 in | 20 TPI | 28 TPI |
| 5/16” | 0.3125 in | 18 TPI | 24 TPI |
| 3/8” | 0.375 in | 16 TPI | 24 TPI |
| 7/16” | 0.4375 in | 14 TPI | 20 TPI |
| 1/2” | 0.500 in | 13 TPI | 20 TPI |
| 5/8” | 0.625 in | 11 TPI | 18 TPI |
| 3/4” | 0.750 in | 10 TPI | 16 TPI |
| 7/8” | 0.875 in | 9 TPI | 14 TPI |
| 1” | 1.000 in | 8 TPI | 12 TPI |
This chart is useful for first checking, but final orders should follow the required ASME, ASTM, SAE, or project standard.
UNC vs UNF: Which One Should Buyers Stock?
UNC Coarse Thread
UNC is common for general industrial use. It is easier to assemble, more tolerant of dirt or minor damage, and widely stocked.
UNF Fine Thread
UNF is often used where finer adjustment, stronger thread engagement, or vibration control is needed. It is common in automotive, machinery, and equipment repair markets.
| Thread Type | Best Use | Buyer Note |
|---|---|---|
| UNC | General assembly, maintenance, construction supply | Usually faster to source |
| UNF | Automotive, equipment repair, precision assemblies | Must confirm mating nut or tapped hole |
| Special inch thread | OEM or legacy equipment | Requires drawing or sample |
For non-standard inch threads or special lengths, use custom non-standard fasteners.
RFQ Checklist for Imperial Fasteners
Before requesting a quote, provide:
- Diameter and length
- UNC, UNF, or special thread
- TPI value
- Head style and drive type
- Material and grade
- Surface finish or coating
- Matching nuts and washers
- Packaging and labeling requirements
For complete sourcing, review the full fastener products range. If washers are included, check washer products for matching sizes.
Final Advice
Imperial fastener sourcing should never rely on visual comparison. Importers and distributors should confirm diameter, TPI, thread series, length, grade, finish, and matching parts before ordering. This prevents wrong-thread inventory and reduces customer complaints.