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Fastener Shank–Head Midpoint Hole Diameter

Calculate the diameter halfway between a positive fastener shank and a larger head in this geometric model.

  • Formula & worked example
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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

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Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

A 6 mm shank and 10 mm head have a midpoint diameter of 8 mm.

Midpoint hole diameter = (shank diameter + head diameter) / 2

Worked example

Enter these known values and leave the other values blank.

Shank diameter
6 mm
Head diameter
10 mm
Geometric midpoint hole diameter
8 mm

Assumptions and limitations

  • The retained equation is a midpoint heuristic. It does not provide standard machining clearance, threaded-hole dimensions or a specified fit class.
  • The head diameter must exceed the positive shank diameter. The midpoint lies between them, leaving a positive geometric head-bearing width.
  • Select actual clearance from the applicable fastener/fit specification when a prescribed tolerance is required.
  • Arithmetic uses 64 significant decimal digits. Displayed results use the configured rounding.

Common questions

Does this calculate an ISO or ASME clearance-hole table value?

This model averages the shank and head diameters. A standard clearance-hole table uses its own specified tolerances and can give a different value.

References

The calculation equations, inverse formulas, units, and input rules were imported from this source. Bookify provides the interface and equation solver.

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