of the raised ribs consists in the direction from the opening 12 side toward the inside bottom of the barrel 11 of an inclined face 20a oriented toward the inside bottom a face 20b parallel to the axis of the barrel 11 a concavely arcuate face 20c a face 20d parallel to the axis and a semi arcuate face 20e inclined toward the inside bottom of the barrel in the manner of a continued range of mountains the three raised ribs are disposed substantially parallel and circumferentially spaced at fixed intervals on the inside wall of the barrel 11 whereby the three parallel faces 20b jointly form a substantially annular step the three arcuate faces 20c form a substantially spherical first cavity 15 the three parallel faces 20d form a second annular step and the three arcuate faces 20e form in conjunction with the inside bottom of the barrel a spherical second cavity 16 further the inclined faces 20 a in the portions of said raised ribs 20 closest to the opening 12 jointly form a guide portion which serves to guide the engaging portion 10 formed at the leading end of the shaft 6 of the male member 1 into the cavity 15 formed.