This is a motor fan mount compatible with both the Tamiya Falcon and the Hirobo Tomcat. You mount it on the rear end of the chassis. It supports 25mm fan.

Version for Falcon: upgradeparts-tami-falcon-motor-fanmount-25mm

Version for Tomcat (with very small difference in size): upgradeparts-tami-falcon-motor-fanmount-25mm-tomcat