Tamiya 9803565 Upper Arm Lock Nut for TRF421X  [9803565]

Durability and fit for TRF421X upper arm

This component is an RC-scale replacement upper arm nut intended for the TRF421X chassis, sold as the Tamiya 9803565 spare part. It secures the upper arm pivot so the suspension geometry remains stable while you fine-tune camber and ride height.

The nut is made to match TRF421X-series suspension assemblies as noted by part reference 42391. When replacing it, hand-start the threads to avoid cross-threading, clean the mating areas, and use the correct hex driver or wrench for the final seating. Avoid over-tightening to prevent damage to plastic or composite arm inserts.

For long-term reliability, the nut keeps pivot location steady under load so alignment and setup remain predictable. Check the nut after any hard hits and confirm thread engagement each time you change arms or other components.