Tamiya 9803478 - Tensioner Nut for TRF421X (42391 compatible)  [9803478]

Replacement tensioner nut, TRF421X fit

This replacement tensioner nut is intended for the 42391 TRF421X assembly and serves to set and retain the tension where the factory nut is located. Its purpose is straightforward: allow repeatable adjustments during setup and routine maintenance.

Practically, the part is used to tune drivetrain belt or linkage tension and to keep consistent clearance in the relevant assembly. As with any direct replacement-style item, confirm that the nut engages properly with the 42391 TRF421X mounting points before finalising the build.

To install, position the nut on the designated threaded interface, turn until the required tension or gap is reached, and check that drivetrain or linkage movement is smooth across its range. After adjustment, re-verify alignment and rotational tension to ensure the setting remains stable.