A clearance hole is the hole a bolt or screw passes through without threading into it. Fastener standards define three fits: close for accurate location, normal (also called free or medium) for general work, and loose (coarse) where holes are drilled in separate parts and may not line up exactly. The tables below give all three for inch machine screws and bolts from #0 to 1 inch and for metric sizes from M1.6 to M30. They are the same values our clearance hole calculator uses.
Inch clearance holes
| Screw or bolt | Major dia (in) | Close fit | Normal fit | Loose fit |
|---|---|---|---|---|
| #0 | 0.0600 | #52 (0.0635) | #50 (0.0700) | #46 (0.0810) |
| #1 | 0.0730 | #48 (0.0760) | #46 (0.0810) | #43 (0.0890) |
| #2 | 0.0860 | #43 (0.0890) | #41 (0.0960) | #37 (0.1040) |
| #3 | 0.0990 | #38 (0.1015) | #36 (0.1065) | #32 (0.1160) |
| #4 | 0.1120 | #32 (0.1160) | #30 (0.1285) | #27 (0.1440) |
| #5 | 0.1250 | #30 (0.1285) | #29 (0.1360) | #23 (0.1540) |
| #6 | 0.1380 | #27 (0.1440) | #25 (0.1495) | #18 (0.1695) |
| #8 | 0.1640 | #18 (0.1695) | #15 (0.1800) | #10 (0.1935) |
| #10 | 0.1900 | #9 (0.1960) | #5 (0.2055) | #2 (0.2210) |
| #12 | 0.2160 | #2 (0.2210) | 7/32" (0.2344) | 1/4" (0.2500) |
| 1/4" | 0.2500 | F (0.2570) | 17/64" (0.2656) | 9/32" (0.2812) |
| 5/16" | 0.3125 | 21/64" (0.3281) | 11/32" (0.3438) | 3/8" (0.3750) |
| 3/8" | 0.3750 | 25/64" (0.3906) | 13/32" (0.4062) | 7/16" (0.4375) |
| 7/16" | 0.4375 | 29/64" (0.4531) | 15/32" (0.4688) | 1/2" (0.5000) |
| 1/2" | 0.5000 | 33/64" (0.5156) | 17/32" (0.5312) | 9/16" (0.5625) |
| 9/16" | 0.5625 | 37/64" (0.5781) | 19/32" (0.5938) | 5/8" (0.6250) |
| 5/8" | 0.6250 | 41/64" (0.6406) | 21/32" (0.6562) | 11/16" (0.6875) |
| 3/4" | 0.7500 | 49/64" (0.7656) | 25/32" (0.7812) | 13/16" (0.8125) |
| 7/8" | 0.8750 | 57/64" (0.8906) | 29/32" (0.9062) | 15/16" (0.9375) |
| 1" | 1.0000 | 1-1/64" (1.0156) | 1-1/32" (1.0312) | 1-1/16" (1.0625) |
Metric clearance holes (ISO 273)
| Size | Bolt dia (mm) | Fine (close) | Medium (normal) | Coarse (loose) |
|---|---|---|---|---|
| M1.6 | 1.6 | 1.7 | 1.8 | 2 |
| M2 | 2 | 2.2 | 2.4 | 2.6 |
| M2.5 | 2.5 | 2.7 | 2.9 | 3.1 |
| M3 | 3 | 3.2 | 3.4 | 3.6 |
| M4 | 4 | 4.3 | 4.5 | 4.8 |
| M5 | 5 | 5.3 | 5.5 | 5.8 |
| M6 | 6 | 6.4 | 6.6 | 7 |
| M8 | 8 | 8.4 | 9 | 10 |
| M10 | 10 | 10.5 | 11 | 12 |
| M12 | 12 | 13 | 13.5 | 14.5 |
| M14 | 14 | 15 | 15.5 | 16.5 |
| M16 | 16 | 17 | 17.5 | 18.5 |
| M20 | 20 | 21 | 22 | 24 |
| M24 | 24 | 25 | 26 | 28 |
| M30 | 30 | 31 | 33 | 35 |
Worked example: how far can two holes be out of line?
When two plates are bolted together with a nut on the back (a “floating” fastener, because the bolt is free in both holes), each hole may be off its true position by up to half the difference between the hole and bolt diameters. The geometric tolerancing formula is T = H − F, where H is the hole diameter and F the fastener diameter, and T is the diameter of the zone the hole centre must fall inside. For a 1/4 in bolt in a normal-fit 17/64" hole (0.2656 in): T = 0.2656 − 0.2500 = 0.0156 in, so each hole centre may be about 0.0078 in off its intended position in any direction.
If one part is tapped instead (a “fixed” fastener, the bolt cannot move in the threaded part), the tolerance has to be shared: T = (H − F) / 2 = 0.0078 in for the same hole. That is why a tapped part plus a clearance part needs more care, or the loose fit. In metric: an M8 bolt in a medium-fit 9 mm hole gives T = 1 mm floating, 0.5 mm fixed.
Which fit to use
- Close: holes drilled through both parts together (match drilling), jigs and fixtures, and anywhere the bolt locates the part. Expect to need a straight, accurately sized drill.
- Normal: the default for machine parts, brackets and enclosures drilled separately with a drill press and a good layout.
- Loose: parts drilled by hand, sheet metal, wood-to-metal assemblies, and long rows of bolts where small errors add up.
- Wood: a bolt through wood needs only a snug clearance hole, typically the bolt diameter plus 1/32 to 1/16 in, so it can be tapped through without splitting. For wood screws use the shank clearance and pilot sizes in our screw and nail size calculator.
Common mistakes
- Drilling the clearance hole with the tap drill: a 1/4-20 bolt will not pass through a #7 hole. Keep the two drills apart, or label them.
- Forgetting the washer and head: a loose-fit hole under a small pan head can leave too little bearing area. Use a washer, or a flange-head screw.
- Countersinking for a flat-head screw without the right clearance hole underneath; the countersink diameter is set by the head, but the hole below it still needs normal clearance for the shank.
Frequently asked questions
What size clearance hole for a 1/4 inch bolt?
17/64" (0.2656 in) for a normal fit, F (0.2570 in) for a close fit and 9/32" (0.2812 in) for a loose fit.
What size clearance hole for an M6 bolt?
6.6 mm for the ISO 273 medium (normal) fit, 6.4 mm fine and 7.0 mm coarse.
What is the difference between a tap drill and a clearance drill?
The tap drill is smaller than the bolt, leaving material for the tap to cut threads into. The clearance drill is larger than the bolt so it slides through.
What does close, normal and loose fit mean?
They are clearance classes: close allows the least play and needs accurate hole positions, normal is the general-purpose default, and loose allows the most misalignment.
Sources and method
Every dimension on this page is computed from the formulas below, not copied from another chart, so you can check any row by hand. Values are basic (nominal) dimensions; real parts are made to tolerance classes (2A/2B for inch, 6g/6H for metric) and are slightly smaller (bolts) or larger (nuts and tapped holes).
- ASME B1.1, Unified Inch Screw Threads (UN and UNR Thread Form): basic profile, pitch-diameter and minor-diameter relationships, and the tensile stress area formula. The same relationships are published in the US federal standard FED-STD-H28/2B, Screw-Thread Standards for Federal Services, Section 2 (a US Government work).
- ISO 68-1, ISO general purpose screw threads, basic profile; ISO 261, general plan of diameters and pitches; ISO 898-1, stress area of metric bolts.
- ASME B94.11M, Twist Drills: number, letter and fractional drill diameters (the drill list used by our calculators).
- ISO 273, Fasteners, clearance holes for bolts and screws (fine, medium, coarse series); inch close / normal / loose fits as published in the ASME B18.2.8 clearance classes and reproduced in fastener suppliers’ charts.
- Percentage-of-thread formula for tap drills: Machinery’s Handbook (Industrial Press), as used by our tap drill size calculator.
More thread and fastener tools
- All thread and fastener charts
- UNC and UNF thread chart
- Metric thread pitch chart
- Tap drill chart (inch and metric)
- Clearance hole chart
- Nail size chart
- Wood screw size chart
- Lag screw pilot hole chart
- Bolt torque chart
- Wrench size chart
- Drill bit size chart
- Thread engagement chart
- Nail gun nail sizes by gauge
- Screw and nail size calculator
- Tap drill size calculator
- Clearance hole size calculator
- Tapped hole depth calculator
Last reviewed: 24 October 2026. How we build and check our data: methodology and corrections. Spotted an error? Please let us know.