Tamiya 9803478 TRF421X Compatibility Tensioner Nut for 42391  [9803478]

TRF421X tension control nut

This replacement tensioner nut is designed for RC use with the 42391 TRF421X assembly. Its role is straightforward: establish and maintain tension at the original nut location so adjustments can be consistently repeated during setup and maintenance.

Typically the part is used to adjust belt or linkage tension and to preserve proper clearance where required. Because it functions as a direct replacement-style component, installers should verify fitment with the 42391 TRF421X mounting points before finishing assembly.

Installation involves seating the nut on the specified threaded point, rotating until the desired tension or clearance is achieved, and confirming smooth operation of the drivetrain or linkage through its range. Recheck alignment and tension under rotation to ensure the setting holds.