Junior tennis racket head size midplus racket head size 645 cm head size inches 100 sq in stringing 16 x 18 playing properties control balance 320 mm recommended height 140 155 cm weight unstrung 256 g grip circumference 100 102 mm racket balance head light grip size l0 frame material graphite shape oval frame profile min 23 mm frame max 23 mm length 66 cm length inches 26 technology wilson blx season 2015 series wilson