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CORE LINKS · DESIGN GUIDES

Fasten into aluminium

Before choosing torque or engagement from nominal diameter alone, identify the clamped parts and the path of force.

Section of a blind tapped joint; complete thread engagement is marked Le. Torque is shown in a separate top view.FpLeTTop viewSection · incomplete threads excluded
Section concept of a blind tapped hole. Le is actual engagement between complete threads; entrance chamfers, incomplete runout and bottom clearance are excluded.

What you will understand

  • Tightening torque versus preload
  • Effective engagement and thread stripping
  • Joint behavior beyond thread strength

Blue: defined conditions · Red: calculated quantities. Diagrams are schematic.

  • T: tightening torque
  • Fp: preload
  • Le: effective engagement

The examples below are illustrative. Calculator links open the normal calculator; enter the listed conditions yourself. Values are not transferred automatically.

Define materials, threads and loads

Strength depends on temper and product condition, even within one aluminium alloy designation. Identify the clamped part and the tapped material separately.

  • Aluminium alloy, temper and temperature; bolt property class
  • Nominal diameter, pitch, pitch diameter and actual engagement
  • External-load direction, cycling, vibration and disassembly frequency

Estimate preload from torque

Tightening stretches the bolt and clamps the parts. Nut factor K is not the thread friction coefficient. Use values and preload scatter appropriate to lubrication, bearing surfaces and finish.

Fp ≈ T / (K d)

Example: understand preload magnitude

Inputs

  • Tightening torque T = 12 N·m
  • Nominal diameter d = 10 mm
  • Nut factor K = 0.20 (assumed)

Results

  • Estimated preload Fp = 6,000 N

12 N·m is not a recommended torque. At the same torque, K = 0.15 gives 8,000 N. Compare the verified range: maximum preload matters for thread/bolt strength, minimum preload for separation and slip.

Check threads and bolt separately

The engagement calculator is an empirical preliminary estimate using effective thread shear area As ≈ π dm Le / 3. It compares female/male thread shear and bolt tension; it does not certify JIS thread grades or detailed thread geometry.

Example: compare maximum load with assumed allowables

Inputs

  • Maximum axial force F = 6,000 N; multiplier k = 1.5
  • Pitch diameter dm = 9.026 mm; pitch p = 1.5 mm; trial Le = 15 mm
  • Assumed allowable shear: female 80 MPa, male 160 MPa
  • Assumed bolt tensile area 58 mm² and allowable tension 300 MPa

Results

  • Comparison load kF = 9,000 N
  • Required engagement ≈ 11.90 mm
  • Round up by pitch: 8 complete pitches / 12 mm

These allowables are illustrative, not recommendations for A5052 or another material. Define k on the load side consistently with margins already in the allowables. A 12 mm engagement is not an unconditional safety decision.

Check the complete joint

External load does not necessarily add directly to one bolt. Load sharing depends on bolt and part stiffness, preload bounds and interface friction.

  • Separation, slip and local bearing pressure
  • Thin-boss splitting, edge distance, bottoming and breakthrough
  • Fatigue, loosening, temperature differences and galvanic corrosion
  • Compare inserts or other methods when repeated disassembly is needed

Keep a review checklist

This checklist is a personal reminder, not a safety score or an automatic approval. It is not sent or saved.

Continue with another guide

Reference information and illustrative calculations. This content does not guarantee suitability or safety of a design. Confirm the actual materials, component specifications and operating conditions.