These are the grommets for the bridge section. To make the strings slide easily, apply a resin protectant (Polyclimate). Applying it to each grommet hole will allow you to feel the ball grip and spin effect. Replacing them is very easy. It might refresh your racket. Two types of grommets are sold for the new Pure Drive. They seem to be quite different. Pure Drive has 3 ridges, and Percept has 4 ridges. The impact of the replacement might be significant.