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 340 mm recommended height from 155 cm weight unstrung 270 g racket balance even grip size l1 l5 frame material graphite shape oval frame profile min 26 mm frame max 28 mm length 695 cm length inches 27 technology head graphene season 2014 series head prestige a