Adult tennis racket head size oversize racket head size 658 cm head size inches 102 sq in stringing 16 x 19 level beginner type of racket comfort racket balance 340 mm recommended height from 155 cm weight unstrung 260 g racket balance even grip size l1 l5 frame material graphite shape oval frame profile min 22 mm frame max 25 mm length 685 cm length inches 27 technology head graphenext season 2016 series head radical