The invention is formed by including a proximal end portion having an inside diameter capable of receiving a member having a shape including a substantially circular outer circumferential portion and a convex portion formed at the outer circumferential portion as an outside diameter shape, and having an outside diameter formed into a shape substantially similar to the outside diameter shape, a distal end portion in a substantially cylindrical shape having an outside diameter that is equal to or larger than a maximum outside diameter of the proximal end portion, and a cutout portion that is formed in a site corresponding to the convex portion, and is in a shape which is cut out from the proximal end portion to the distal end portion.
