Adult tennis racket head size midsize racket head size 613 cm head size inches 95 sq in stringing 18 x 20 level professional type of racket tournament racket playing properties control power balance 330 mm weight unstrung 289 g racket balance even grip size l1 l3 shape oval frame profile min 22 mm frame max 22 mm length 686 cm technologies wilson blx wilson double hole technology wilson parallel drilling season 2017 series wils