Materials: Hogad curtain rod, Raffig curtain rod caps
Description: For my sons race car themed bedroom, I took two gray Raffig curtain end caps and with a pair of pliers pried off the rounded portion. (Note: The Raffig end cap is two pieces held together by glue). I then took two Ridemakerz wheels and hollowed them out with an Exacto knife. The wheel and the cap were a perfect fit. Add a little glue.
Simple. Easy. Done.