Spiralock Thread Locking: Why It Beats Spring Washers 10×

Why do ordinary bolts loosen under vibration? Do spring washers actually work? Spiralock threads offer a more fundamental solution.

Why Ordinary Threads Loosen

In standard V-threads, the contact surface is radial. Under vibration, micro-slip between thread flanks causes gradual loss of axial preload. NASA-STD-5020 explicitly states that spring washers and nylon insert nuts are "preload-dependent" locking methods with limited effectiveness under sustained vibration.

How Spiralock Works

Spiralock adds a 30-degree wedge ramp at the minor diameter of the internal thread (standard threads have a flat or rounded root). When a standard bolt is screwed in, the bolt crest is pressed against this ramp, creating a radial locking force.

Key difference:

• Standard threads: locking depends on axial clamp force. Once axial force drops under vibration, it loosens.
• Spiralock: locking force is radial and does not depend on axial preload. Even if all axial preload is lost, the radial lock remains — the bolt won't self-loosen.

Performance Comparison (Junker Vibration Test)

• Standard threads + spring washer: 50% preload loss in 2–3 minutes
• Nylon insert lock nut: 50% loss in 10–15 minutes
• Spiralock: virtually no preload loss after hundreds of vibration cycles

This is why Spiralock is used in aerospace, automotive, and rail — it's one of the locking methods recognized under NASA's low-fatigue-risk clause.

Usage Notes

1. Spiralock modifies the internal thread only. Use a standard bolt — cost is in the nut or tapped hole

2. Installation torque is 10–20% higher than standard threads (due to radial interference)

3. Reusable — unlike nylon nuts that wear out

4. Standard external bolt required — no special bolt needed

Toprecision supplies Spiralock nuts and wire thread inserts for robot joints, motors, and vibrating equipment.