This is an optional Tekno RC Elektri-Clutch Adapter, and is intended for use with the Traxxas Revo equipped with the Tekno RC Brushless conversion. The patent pending Tekno RC Elektri-Clutch clutch bell adapter is one of the most innovative products to come along in years for electric enthusiasts. It allows you to use any Revo/Maxx style clutch and clutch bell setup currently available on any motor that has a 5mm diameter motor shaft.
It can be used for other applications besides the Tekno RC Brushless Conversion for Revo, but Tekno does not directly support other applications outside of the Tekno RC Brushless conversion. You may need to modify and/or produce a motor mount suitable for Elektri-Clutch use if you are using it elsewhere.