Adult tennis racket head size oversize racket head size 690 cm head size inches 107 sq in stringing 16 x 19 level beginner type of racket comfort racket balance 330 mm recommended height from 155 cm weight unstrung 280 g racket balance even grip size l0 l5 shape oval frame profile min 23 mm frame max 26 mm length 69 cm length inches 27 technology head graphene season 2015 series head effortless power additional information