PURPOSE:To surely eliminate various length of waste thread which would cause coiling of thread around an axle by providing an ward protruding part on a supporting yoke and ward protruding parts on a protection disk. CONSTITUTION:A protection disk 2 is provided between a wheel 2 and a supporting yoke 4 so that the protection part covers an axle part. Outward protruding parts 3 are provided at equal intervals on the periphery edge part 22 of the protection disk 2, and plate-shape collars 31 are formed on the tip ends of the outward protruding parts 3 to hook coiled waste thread so that the waste thread does not come off. Next, a long hole h is bored on the supporting yoke 4 at the position shorter than a radius from an axle 13 to the outward protruding parts 3 provided on the protection disk 4, an an inward protruding part 5 is set slidably in up and down directions on the long hole h. Thereby if waste thread is long, it is coiled around the outward protruding parts 3, and is not, it invades to the axle side but it is coiled around the inward protruding parts 5.
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