Calculate thread insert

Size a printed boss and blind hole for a heat-set threaded insert.

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ToolThread Insert Calculator
Input
Output
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Preview

How it works

Hole diameter subtracts radial clearance from insert outer diameter, and hole depth adds a drilling margin to insert length. Boss diameter is the larger of hole diameter plus twice the minimum wall or twice the insert diameter.

  • 0.2 mm clearance, 0.5 mm depth margin, and 2.5 mm wall are starting values.
  • Fit depends on printer calibration and material strength.

Worked example

A common M3 knurled brass insert
4.0mm outer diameter, 5.7mm long
Input
											Insert outer diameter mm: 4
Insert length mm: 5.7
Output
												Hole diameter mm: 3.8
Hole depth mm: 6.2
Recommended boss diameter mm: 8.8
Wall thickness mm: 2.5

When to use this

Printed enclosures, repairable brackets, and M3 insert bosses use these dimensions.

Edge cases

  • Too little clearance can split a boss during heat setting.
  • A blind hole needs depth margin for debris and insertion error.
  • A thin wall can crack even when diameter arithmetic is correct.