Junior tennis racket head size oversize racket head size 645 cm head size inches 100 sq in stringing 16 x 19 playing properties comfort control recommended height 140 155 cm weight unstrung 250 g stiffness 66 ra grip size l0 l2 frame material graphite shape oval frame profile min 22 mm frame max 22 mm length 66 cm length inches 26 season 2017 player novak djokovic series head speed colour black additional information t