This is a stepper motor mount for 2020 extrusions. This design is for 40mm long stepper motors.
There are two models. One with a place for the wire to fit and one without. DONT GET THE WIRE JAMMED. If you get it jammed you will need to break apart the print with pliers to get the motor out.
Its designed this way so it doesn't extrude from the confines of the 3d printer which I an building.