Adult tennis racket head size midplus racket head size 645 cm head size inches 100 sq in stringing 16 x 19 levels professional advanced type of racket all round racket balance 320 mm recommended height from 155 cm weight unstrung 310 g racket balance head light shape oval frame profile min 23 mm frame max 23 mm length 68 cm length inches 27 series dunlop biomimetic