This invention relates to a top end stop having a substantially U-shaped section and a bottom end stop having a substantially lateral-H shaped section. In each end stop, leg portions having key-shaped sections, i.e., a hook shaped portion is provided at front ends thereof, are extended in a bent manner from a rectangular base portion, so that an accommodation portion surrounded by the base portion and a pair of leg portions is provided for accommodating a core portion. A row of a projecting portion is formed continuously/intermittently on an inner face of the base portion and a gap portion is provided between the projecting portion and the root of each leg portion. The projecting portion positions the core portion accurately and holds it, and in crimping the leg portions, the core portion is compressed, and the gap portion is filled thereby, so that the core portion is secured firmly.