Junior tennis racket head size midsize racket head size 613 cm head size inches 95 sq in stringing 16 x 17 balance 270 mm recommended height 116 128 cm weight unstrung 194 g grip circumference 100 102 mm racket balance head light grip size l0 frame material titanium shape oval frame profile min 19 mm frame max 19 mm length 584 cm length inches 23 technology wilson quadriform technology player roger federer series wilson j