Clearance Hole Chart
Look up verified clearance hole diameters and recommended standard drill bits for inch-series fasteners (ASME B18.2.8) and metric bolts (ISO 273).
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Common Fasteners:
Standard Fastener Clearance Table
Fastener Clearance Hole Reference Chart
Imperial (ASME B18.2.8 Close / Normal / Loose) and Metric (ISO 273 Fine / Medium / Coarse)
| Fastener Size | Standard | Nominal Dia | Close / Fine Drill (Dia) | Normal / Medium (Standard) Drill (Dia) | Loose / Coarse Drill (Dia) | Copy |
|---|---|---|---|---|---|---|
| #0 | ASME B18.2.8 | 0.0600" | #51 0.0670" | #49 0.0730" | #46 0.0810" | |
| #1 | ASME B18.2.8 | 0.0730" | #47 0.0785" | #43 0.0890" | #39 0.0995" | |
| #2 | ASME B18.2.8 | 0.0860" | #43 0.0890" | #36 0.1065" | #31 0.1200" | |
| #3 | ASME B18.2.8 | 0.0990" | #38 0.1015" | #32 0.1160" | #29 0.1360" | |
| #4 | ASME B18.2.8 | 0.1120" | #32 0.1160" | #30 0.1285" | #27 0.1440" | |
| #5 | ASME B18.2.8 | 0.1250" | #29 0.1360" | #25 0.1495" | #19 0.1660" | |
| #6 | ASME B18.2.8 | 0.1380" | #27 0.1440" | #20 0.1610" | #16 0.1770" | |
| #8 | ASME B18.2.8 | 0.1640" | #18 0.1695" | #11 0.1910" | #4 0.2090" | |
| #10 | ASME B18.2.8 | 0.1900" | #9 0.1960" | #2 0.2210" | 1/4" 0.2500" | |
| #12 | ASME B18.2.8 | 0.2160" | #1 0.2280" | 1/4" 0.2500" | 9/32" 0.2812" | |
| 1/4" | ASME B18.2.8 | 0.2500" | F 0.2570" | H 0.2660" | 9/32" 0.2812" | |
| 5/16" | ASME B18.2.8 | 0.3125" | P 0.3230" | Q 0.3320" | 11/32" 0.3438" | |
| 3/8" | ASME B18.2.8 | 0.3750" | W 0.3860" | X 0.3970" | 27/64" 0.4219" | |
| 7/16" | ASME B18.2.8 | 0.4375" | 29/64" 0.4531" | 15/32" 0.4688" | 1/2" 0.5000" | |
| 1/2" | ASME B18.2.8 | 0.5000" | 33/64" 0.5156" | 17/32" 0.5312" | 9/16" 0.5625" | |
| 9/16" | ASME B18.2.8 | 0.5625" | 37/64" 0.5781" | 19/32" 0.5938" | 5/8" 0.6250" | |
| 5/8" | ASME B18.2.8 | 0.6250" | 41/64" 0.6406" | 21/32" 0.6562" | 11/16" 0.6875" | |
| 3/4" | ASME B18.2.8 | 0.7500" | 49/64" 0.7656" | 25/32" 0.7812" | 13/16" 0.8125" | |
| 7/8" | ASME B18.2.8 | 0.8750" | 57/64" 0.8906" | 29/32" 0.9062" | 15/16" 0.9375" | |
| 1" | ASME B18.2.8 | 1.0000" | 1-1/16" 1.0625" | 1-1/8" 1.1250" | 1-3/16" 1.1875" | |
| M1.6 | ISO 273 | 1.60 mm | 1.70 mm 1.70 mm | 1.80 mm 1.80 mm | 2.00 mm 2.00 mm | |
| M2 | ISO 273 | 2.00 mm | 2.20 mm 2.20 mm | 2.40 mm 2.40 mm | 2.60 mm 2.60 mm | |
| M2.5 | ISO 273 | 2.50 mm | 2.70 mm 2.70 mm | 2.90 mm 2.90 mm | 3.10 mm 3.10 mm | |
| M3 | ISO 273 | 3.00 mm | 3.20 mm 3.20 mm | 3.40 mm 3.40 mm | 3.60 mm 3.60 mm | |
| M3.5 | ISO 273 | 3.50 mm | 3.70 mm 3.70 mm | 3.90 mm 3.90 mm | 4.20 mm 4.20 mm | |
| M4 | ISO 273 | 4.00 mm | 4.30 mm 4.30 mm | 4.50 mm 4.50 mm | 4.80 mm 4.80 mm | |
| M5 | ISO 273 | 5.00 mm | 5.30 mm 5.30 mm | 5.50 mm 5.50 mm | 5.80 mm 5.80 mm | |
| M6 | ISO 273 | 6.00 mm | 6.40 mm 6.40 mm | 6.60 mm 6.60 mm | 7.00 mm 7.00 mm | |
| M7 | ISO 273 | 7.00 mm | 7.40 mm 7.40 mm | 7.60 mm 7.60 mm | 8.20 mm 8.20 mm | |
| M8 | ISO 273 | 8.00 mm | 8.40 mm 8.40 mm | 9.00 mm 9.00 mm | 10.00 mm 10.00 mm | |
| M10 | ISO 273 | 10.00 mm | 10.50 mm 10.50 mm | 11.00 mm 11.00 mm | 12.00 mm 12.00 mm | |
| M12 | ISO 273 | 12.00 mm | 13.00 mm 13.00 mm | 13.50 mm 13.50 mm | 14.50 mm 14.50 mm | |
| M14 | ISO 273 | 14.00 mm | 15.00 mm 15.00 mm | 15.50 mm 15.50 mm | 16.50 mm 16.50 mm | |
| M16 | ISO 273 | 16.00 mm | 17.00 mm 17.00 mm | 17.50 mm 17.50 mm | 18.50 mm 18.50 mm | |
| M18 | ISO 273 | 18.00 mm | 19.00 mm 19.00 mm | 20.00 mm 20.00 mm | 21.00 mm 21.00 mm | |
| M20 | ISO 273 | 20.00 mm | 21.00 mm 21.00 mm | 22.00 mm 22.00 mm | 24.00 mm 24.00 mm | |
| M22 | ISO 273 | 22.00 mm | 23.00 mm 23.00 mm | 24.00 mm 24.00 mm | 26.00 mm 26.00 mm | |
| M24 | ISO 273 | 24.00 mm | 25.00 mm 25.00 mm | 26.00 mm 26.00 mm | 28.00 mm 28.00 mm |
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Understanding Clearance Hole Fit Classes
Fastener clearance holes allow the unthreaded shank or threaded body of a bolt or screw to freely pass through a through-hole without binding or requiring threading.
- Close Fit (Inch) / Fine Series (ISO): Intended for precision assemblies where minimal positional play or accurate alignment is required. Fastener heads must sit fully flat against the mating surface.
- Normal Fit (Inch) / Medium Series (ISO): The standard workshop recommendation for general industrial assembly. Provides adequate clearance for normal positional tolerance variations.
- Loose Fit (Inch) / Coarse Series (ISO): Intended for applications with wide positional tolerances, multi-fastener patterns on fabricated or cast parts, or where quick field assembly without binding is needed.
Tap Holes vs. Clearance Holes
1. Tap Hole (Internal Threading): Drilled smaller than the screw's major diameter so that a tap tool can cut mating threads into the material core. (e.g., 1/4"-20 tap hole uses a #7 drill = 0.2010").
2. Clearance Hole (Pass-Through): Drilled larger than the screw's major diameter so the fastener slides smoothly through the through-plate. (e.g., 1/4" normal clearance hole uses an 'H' drill = 0.2660").
Fastener Clearance Standards
View Full Methodology →- ASME B18.2.8 – Clearance Holes for Bolts, Screws, and Studs: Recommended standard hole sizes for inch-series fasteners categorized into Close, Normal, and Loose fit clearance.
- ISO 273 – Fasteners: Clearance Holes for Bolts and Screws: International standard for metric fastener clearance holes categorized into Fine, Medium, and Coarse series.
- Machinery's Handbook (31st Edition): Standard reference work for mechanical engineers, designers, manufacturing engineers, and machinists.
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