Ford Mustang Rear Bumper Chrome Letters Insert These Mustang Rear Bumper Enhancement Letters (99-04), which are bombarded by rain, sun, and cold, use 3M adhesive. Designed to fit neatly into the rear bumper filler indents these letters are easy to install - just clean, peel the 3M adhesive and press into place with a 3D relief. Color: Chrome. 1/8" thickness.