Adult tennis racket head size midplus racket head size 645 cm head size inches 100 sq in stringing 16 x 19 16 x 16 type of racket tournament racket playing properties comfort control power spin balance 330 mm recommended height from 155 cm weight unstrung 305 g racket balance even grip size l0 l5 shape oval length 685 cm length inches 27 technology head graphene touch season 2017 player maria sharapova