Product review (5 stars): look up your part number first!
To know whether the cap fits your kitchenaid dishwasher, visit http://www.kitchenaid.com/customer-service/manuals/ and enter the model number for your dishwasher, like KUDI02IRBS2. The model number is on a sticker on the inside of the dishwasher on the left front side of the tub.  The parts list manual for your model will tell you the exact part number for the rise aid cap.