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Look up recommended clearance hole diameters for metric and inch bolts and screws — three fit types per size, per ISO 273:2017 and ASME B18.2.8-1999 (R2017). A clearance hole allows the bolt shank to pass through freely without threading.

Bolt and Screw Clearance Hole Calculator

Look up clearance hole diameters for metric and imperial bolts and screws with close, normal and loose fit references.

Calculator

Nominal diameter: 6 mm · Standard: ISO 273:2017

Clearance hole diagram — bolt passing through a clearance hole

A clearance hole (d₂) is drilled larger than the bolt shank (d) so the fastener passes through freely. The nut or threaded component on the other side provides the clamping force.

Series 1 — H12
Close Fit
Fine / Precision
6.4
mm
Clearance: +0.4 mm
Rec. drill: 6.4 mm

Minimum clearance. Used where accurate location of parts is required. Requires careful alignment during assembly.

Series 2 — H13
Normal Fit
Medium
6.6
mm
Clearance: +0.6 mm
Rec. drill: 6.6 mm

Standard clearance for general-purpose assemblies. Most commonly used. Allows slight misalignment.

Series 3 — H14
Loose Fit
Coarse
7.0
mm
Clearance: +1.0 mm
Rec. drill: 7 mm

Maximum clearance. Easy assembly, tolerates significant misalignment. Used where frequent assembly/disassembly is needed.

Full Reference Table

— ISO 273:2017

All dimensions in mm. Switch standard above to toggle between metric and imperial. Highlighted row = currently selected size.

SizeNominal
(mm)		Close Fit
Series 1 · H12		Normal Fit
Series 2 · H13		Loose Fit
Series 3 · H14		+Clearance
(Normal)		Rec. Drill
(Normal fit)
M11.01.11.21.3+0.21.2 mm
M1.21.21.31.41.5+0.21.4 mm
M1.41.41.51.61.8+0.21.6 mm
M1.61.61.71.82.0+0.21.8 mm
M22.02.22.42.6+0.42.4 mm
M2.52.52.72.93.1+0.42.9 mm
M33.03.23.43.6+0.43.4 mm
M3.53.53.73.94.2+0.43.9 mm
M44.04.34.54.8+0.54.5 mm
M55.05.35.55.8+0.55.5 mm
M66.06.46.67.0+0.66.6 mm
M77.07.47.68.0+0.67.8 mm
M88.08.49.010.0+1.09 mm
M1010.010.511.012.0+1.011 mm
M1212.013.013.514.5+1.513.5 mm
M1414.015.015.516.5+1.515.5 mm
M1616.017.017.518.5+1.517.5 mm
M1818.019.020.021.0+2.020 mm
M2020.021.022.024.0+2.022 mm
M2222.023.024.026.0+2.024 mm
M2424.025.026.028.0+2.026 mm
M2727.028.030.032.0+3.030 mm
M3030.031.033.035.0+3.033 mm
M3333.034.036.038.0+3.036 mm
M3636.037.039.042.0+3.040 mm
M3939.040.042.045.0+3.042 mm
M4242.043.045.048.0+3.045 mm
M4545.046.048.052.0+3.048 mm
M4848.050.052.056.0+4.052 mm
M5252.054.056.062.0+4.056 mm
M5656.058.062.066.0+6.062 mm
M6060.062.066.070.0+6.066 mm
M6464.066.070.074.0+6.070 mm
M6868.070.074.078.0+6.074 mm

Click any row to update the results above. All hole diameters are minimum values — actual drill sizes may vary by availability.

Which Fit Type to Choose?

Close Fit

Use when:

  • •High precision location required
  • •Load-bearing shear joints
  • •Reamed holes, precision fixtures
  • •Alignment-critical assemblies

Normal Fit

Use when:

  • •General-purpose bolted joints
  • •Standard structural connections
  • •Most machine assemblies
  • •Default choice when unsure

Loose Fit

Use when:

  • •Rapid or field assembly
  • •Painted/coated bolt shanks
  • •Frequent disassembly expected
  • •Slight misalignment tolerated

Standards Reference

  • ISO 273:2017 — Fasteners: Clearance holes for bolts and screws. Defines three series: Fine (H12), Medium (H13), Coarse (H14), for M1 through M68.
  • ASME B18.2.8-1999 (R2017) — Clearance Holes for Bolts, Screws and Studs. Covers close, normal and loose fits for #0 through 1½″ unified (UNC/UNF) fasteners.
  • Clearance hole (通孔) vs tapped hole (螺纹孔): A clearance hole passes the full bolt shank through without threading — the nut (or tapped plate on the other side) provides clamping.
  • Drill selection: Hole diameters listed are the minimum specified clearance. Choose the nearest standard drill size equal to or larger than the listed value.
  • Coatings: For hot-dip galvanized or heavily coated fasteners, increase hole size by one step (e.g., from Normal to Loose fit) to allow for coating buildup on the bolt shank.