Grommet sets are the plastic components located on the top of the racket and around the head and throat, which insert into the holes in the frame in order to protect the strings. Over time, the grommet sets can get worn over time and need to be replaced. The typical areas of the grommet set that wear out are the bumper strip at the top of the head and occasionally the grommet holes, which can crack / split and lead to premature string breakage.