Abstract: The present invention incorporates a nipple to be inserted inside a hose and a sleeve formed concentrically with the nipple. An annular groove is formed on the outer periphery of the nipple to receive the expanded portion of the rubber toward the tip end of the nipple when the sleeve is caulked and to prevent the rubber from bulging at the tip end of the nipple. The annular groove is configured so that it can receive a portion of the inner rubber wall of hose when the hose is inserted between the nipple and the sleeve when the latter is caulked. The annular groove may be located on the outer periphery of the nipple, such as at a position offset from being in-line with where the sleeve is caulked and nearer to the tip end of the nipple. The number of annular grooves is not limited to one, and may be plural. When plural grooves are formed, they may be arranged adjacent to each other or spaced at a given interval.