Adult tennis racket head size oversize racket head size 742 cm head size inches 115 sq in stringing 16 x 19 level beginner type of racket comfort racket balance 345 mm recommended height from 155 cm weight unstrung 255 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 2015 series head speed spec