molded from a suitable plastic material comprises a collar 39 of generally part cylindrical configuration having a part cylindrical inner surface 41 a leg 43 coupled to the collar and having a cavity 45 therein opening away from the collar the coupling also has resilient wings 47 in the form of elongated slats coupled to the collar 39 on opposite sides of the leg 43 and extending generally in the same direction as the leg 43 in the embodiment illustrated the wings 47 project substantially beyond the end of the leg 43 and they lie generally in the same plane the wings 47 in the embodiment illustrated are essentially flat so as to have an outer flat surface 49 for internally supporting and shaping the sleeve 25 as shown in fig4 the leg 43 terminates inwardly in an end wall 51 although the collar 39 in the embodiment illustrated extends for less than 360 degrees it could if desired extend for a full 360 degrees however it preferably extends for at least about 180 degrees and in the embodiment illustrated it extends for slightly over 180 degrees this enables the collar 39 to be snap fit onto the mast 15 although the coupling 37 could be integrally constructed in the embodiment illustrated it comprises coupling sections 53 and 55 which are mirror images of each other each of the coupling sections comprises a collar section 57 a leg section 59 and one of the wings 47 the coupling sections 53 and 55 can be joined together with the leg sections 59 in confronting relationship in any suitable manner such as by rivets 61 fig3 which extend between flanges 63 of the leg sections 59 in use the leading edge portion of one of.