Adult tennis racket head size midsize racket head size 600 cm head size inches 93 sq in stringing 16 x 19 level professional type of racket tournament racket balance 315 mm recommended height from 155 cm weight unstrung 300 g racket balance head light grip size l0 l5 frame material graphite shape oval frame profile min 20 mm frame max 20 mm length 685 cm length inches 27 technology head graphene season 2015 series head p