This is a custom designed 42mm Crush Cage for the Stryfe that has been adapted to use these:
https://www.gearbest.com/motor/pp_1069422.html?wid=1433363
Brushless motors, the wheels SHOULD fit on top of the body of the motor and provide much more crush and less dart wear than just the outrunner alone
THIS HAS NOT BEEN PRINTED SO I CANNOT GUARANTEE IT WILL WORK 100%