On the other hand, the turn attachment 38 is a member formed into a cylindrical shape, as shown in FIGS. 21A and 21B, for example, from a synthetic resin, and has radial slits 38a in its surface shown in FIG. 21A, with its back shown in FIG. 21B being formed so that the turn attachment 38 can be fitted over the through-packing 12.