Clearance Hole Calculator
Calculate the optimal clearance hole size for screws and bolts using fastener and head diameters
Calculate Clearance Hole Size
Diameter of the screw or bolt shank
Diameter of the screw or bolt head
Clearance Hole Results
Formula used: CH = (DF + DH) / 2
Input values: Fastener: 0.00mm, Head: 0.00mm
Fit classification: No classification
Drill recommendation: Enter fastener dimensions
Hole Size Analysis
Example Calculations
Example 1: M8 Bolt
Fastener diameter (DF): 8 mm
Head diameter (DH): 13 mm
Material: Standard hex head bolt
Calculation
CH = (DF + DH) / 2
CH = (8 mm + 13 mm) / 2
CH = 21 mm / 2
CH = 10.5 mm
Example 2: 6-32 Screw (Imperial)
DF = 0.1380", DH = 0.270"
CH = (0.1380" + 0.270") / 2 = 0.204"
Clearance Fit Types
Close Fit
Tight clearance, minimal play
Ratio: ≤ 1.1
Normal Fit
Standard clearance for most applications
Ratio: 1.1 - 1.3
Loose Fit
Large clearance, easy assembly
Ratio: > 1.3
Common Fasteners
Metric Bolts
M6: 6mm dia, 10mm head
M8: 8mm dia, 13mm head
M10: 10mm dia, 16mm head
M12: 12mm dia, 18mm head
Imperial Screws
#6-32: 0.138" dia, 0.270" head
#8-32: 0.164" dia, 0.320" head
#10-24: 0.190" dia, 0.370" head
1/4"-20: 0.250" dia, 0.438" head
Drilling Tips
Use a pilot hole for larger clearance holes
Deburr holes after drilling for smooth fit
Consider material thickness for countersinking
Account for material expansion in outdoor applications
Understanding Clearance Holes
What is a Clearance Hole?
A clearance hole is a hole through a material that allows the threads of a screw or bolt to pass through without the threads biting into the material. This enables proper fastening without damage to the substrate.
Why Proper Sizing Matters
- •Prevents thread damage during insertion
- •Allows for proper fastener tension
- •Accommodates material expansion and contraction
- •Ensures proper load distribution
Clearance Hole Formula
CH = (DF + DH) / 2
- CH: Clearance Hole diameter
- DF: Diameter of the fastener shank
- DH: Diameter of the fastener head
ASME Standards
The American Society of Mechanical Engineers (ASME B18.2.8) establishes standard clearance hole sizes for both metric and imperial fasteners in close, normal, and loose-fit categories.
Note: This calculator provides estimations typically in the "loose fit" category. Consult ASME B18.2.8 charts for exact specifications.