To prevent a reinforcing core member deviated to a place close to the inner side surface of a locking part from being worn by the preventive fittings.

In the fixing fittings 30 formed out of a plate, sheet shaped rubber 40a as thin as 0.7 to 1.5mm is bonded to the inner surface of a slip preventing main body contact bonding part 31 as a vulcanized rubber member 40. And in the fixing fitting 30a formed out of a bar stock, tube shaped rubber 40b as thin as 0.7 to 1.5mm is inserted to the outer circumferential surface of a slip preventing main body contact bonding part 31a so as to be closely attached thereto. When the fixing fittings mentioned above is bonded onto the locking part of a current slip preventing main body with pressure, the rubber member is brought into a condition that it is positively interposed between a reinforcing core member and fixing fittings.