Rubber wheel that blade goes on, how do I replace

The piece that you need is referred to as the coupler. The coupler is a breakway part that is designed to shear and/or wear down in the event that the blender is overloaded. This is to avoid damage to the motor.

The coupler may be purchased individually and is an easy repair that can be done at home. You may purchase the part and access step-by-step replacement instructions at the following link:

http://www.mendingshed.com/kacoupling.html