US Fastener Sizes and Conversion Charts (Screw, Bolt, Fraction & Metric Equivalents)
US Fastener Sizes and Conversion Charts
Choosing the correct fastener size can be confusing, especially when moving between US screw sizes, fractional inches, and metric equivalents. Whether you’re measuring with calipers, drilling pilot holes, or matching hardware, having an accurate reference is essential. This guide provides handy conversion charts and answers common questions to simplify your project planning.
US Screw Size Conversion Chart
Use this chart to compare US screw numbers to their decimal (inch), fractional, and metric (mm) equivalents.
| Screw Size | Inch Decimal | Nearest Fraction | Metric Equivalent |
|---|---|---|---|
| #0 | 0.060 in. | 1/16" | 1.52 mm |
| #1 | 0.073 in. | 5/64" | 1.85 mm |
| #2 | 0.086 in. | 3/32" | 2.18 mm |
| #3 | 0.099 in. | 7/64" | 2.51 mm |
| #4 | 0.112 in. | 7/64" | 2.84 mm |
| #5 | 0.125 in. | 1/8" | 3.18 mm |
| #6 | 0.138 in. | 9/64" | 3.51 mm |
| #8 | 0.164 in. | 5/32" | 4.17 mm |
| #10 | 0.190 in. | 3/16" | 4.83 mm |
| #12 | 0.216 in. | 7/32" | 5.49 mm |
| #14 | 0.250 in. | 1/4" | 6.35 mm |
US Fraction to Metric Conversion Chart
Common fractional sizes converted to millimeters. Helpful when you only have fractional drill bits or need to approximate metric equivalents.
| US Fraction | Metric (mm) | US Fraction | Metric (mm) | |
|---|---|---|---|---|
| 1/16" | 1.59 mm | 1-3/8" | 34.93 mm | |
| 1/8" | 3.18 mm | 1-1/2" | 38.10 mm | |
| 3/16" | 4.76 mm | 1-5/8" | 41.28 mm | |
| 1/4" | 6.35 mm | 1-3/4" | 44.45 mm | |
| 5/16" | 7.94 mm | 1-7/8" | 47.63 mm | |
| 3/8" | 9.53 mm | 2" | 50.80 mm | |
| 7/16" | 11.11 mm | 2-1/4" | 57.15 mm | |
| 1/2" | 12.70 mm | 2-1/2" | 63.50 mm | |
| 9/16" | 14.29 mm | 2-3/4" | 69.85 mm | |
| 5/8" | 15.88 mm | 3" | 76.20 mm | |
| 11/16" | 17.46 mm | 3-1/4" | 82.55 mm | |
| 3/4" | 19.05 mm | 3-1/2" | 88.90 mm | |
| 7/8" | 22.23 mm | 3-3/4" | 95.25 mm | |
| 1" | 25.40 mm | 4" | 101.6 mm | |
| 1-1/4" | 31.75 mm |
Frequently Asked Questions
- Why are there different screw size standards?
Because regional systems evolved separately. The US uses Imperial sizes, while most of the world uses Metric standards.
- How do I measure screw size accurately?
Use digital calipers for diameter and length. Conversion charts then help match the correct equivalent size.
- What do the numbers on screws mean?
Numbers like #6 or #8 refer to the screw diameter. Higher numbers mean larger diameters.
- Can I use a screw size chart for bolts too?
Yes—bolts follow similar measurement standards. Always confirm application requirements first.
- How do fastener sizes affect load-bearing capacity?
Larger diameters typically support more load due to greater surface area and strength. Always consult engineering data for critical applications.
- Why match screw sizes with pilot holes?
It prevents splitting or weakening the material. Incorrect pilot hole sizing reduces strength and can cause failures.
- What are considerations for outdoor fasteners?
Choose corrosion-resistant materials like stainless steel or coated fasteners. Ensure they withstand moisture and weather exposure.
- How do I determine thread pitch?
Thread pitch is the distance between thread peaks. Use a pitch gauge or ruler to measure accurately.
Final Note
Understanding fastener sizes helps you select the right hardware every time. For a complete range of US bolts, screws, and nuts, visit Monster Bolts.