Bumper Guard / Grommet Set Prince O3 Speedport Silver OS 118 A strip of plastic material containing small tubes that run through the string holes of the racquet frame. These tubes protect the strings from rubbing against the abrasive frame material. The outer, flat surface of wider grommet strips also acts as a bumper guard and serves to protect the upper half of the racquet head from bangs scratch and scrapes. Replacing your old or broken grommets will help to increase string life and can prolong the life of your racquet frame. Please note: The image shown is a generic photo displayed of the racket that the bumper guard sets fit.