Contractable winding mandrel

In a contractable winding mandrel for forming yarn balls and comprising a fix-on piece mounted upon a shaft, first arms articulated thereon, struts rotatably connected to said arms and arranged generally parallel to the shaft, and second arms which are pivotally connected to the struts at their one ends and having their other ends pivotally mounted in a head piece supported on a rod extending axially outwardly of said shaft and which is slidable parallel and coaxially to the shaft, so that when the spacing between the fit-on piece and the head piece is increased or reduced the radial spacing of the struts can be reduced or increased respectively and a ring slidable on said rod pivotally receiving first ends of cross trusses the other ends of which are pivotally connected to the respective struts, the improvement comprising that the outside surface of the fit-on piece is provided with a knurling and at least the second arms are provided with teeth to prevent slipping of yarn upon the mandrel when the spacing between the fit-on piece and the head piece is increased, and a spacer mounted on said rod at a location at which said second arms bear thereagainst when the mandrel is contracted, the radial dimension of said spacer being such as to space said struts from said rod and from said ring when said second arms bear against said spacer.