Tamiya 9803565 - Upper Arm Nut (42391) for TRF421X  [9803565]

Upper arm nut for TRF421X

This is an RC-scale replacement upper arm nut for the TRF421X chassis, provided as the Tamiya 9803565 spare part. It serves as the fastening element at the upper arm pivot, keeping the suspension geometry fixed while you set ride height, camber, and other fine adjustments.

Compatibility is with TRF421X-series suspension assemblies as indicated by the part reference 42391. When replacing this nut, start threads by hand to avoid cross-threading, make sure mating surfaces are clean, and use the appropriate hex driver or wrench for final snugging. Avoid over-tightening which can damage plastic or composite arm inserts.

For tuning and setup, the nut’s role is to hold pivot position under load so alignment changes you make at the shock and turnbuckle remain consistent. Check the nut periodically during practice laps, and re-check thread engagement when swapping arms or replacement components.