The wheel covers are a challenge to attach to the wheels. I machined aluminum plugs with 1/4x20 threaded hole in center to go on the inside of the wheels and glued them in with silicon rubber . Then used 1 3/4" 1/4"x 20 thread machine screwed into plug through 1/4" fender washer, 3/16" x 18 1/4" LEXAN Plastic cover and 1/2" Nylon bushing. Also put Nylon 1/4" x 20- 1 1/2" screw about 1 1/2" from edge through LEXAN to keep cover from spinning. Link
https://fordcmaxhybridforum.com/topi...ge/4/#comments about halfway down the page.
I gained 2 mpg from adding wheel covers and rear wheel well cover.
Paul