313 with the slider pocket block 310 stopping after coming into abutting contact with an overhead plate 410 however the upper ends 325 326 of legs provided on the slider holder case 313 continue to rise to eventually close the l shaped rocking guides 401 402 against the force of the coil spring 404 this corresponds to the step illustrated in fig1 b iv when the slider holder case 313 reaches top dead center the roller 319 rides up and beyond the flat portion 321 of the cam 320 and is seated in a comparatively deeply recessed portion of the cam whereby the pull tab pressing lever 318 which was pivoted to the left in step iii is pivoted to the right or clockwise direction to again press the pull tab p of the slider s against the wall of the slider pocket block 310 at the same time the upper ends 325 326 of the legs of slider holder case 313 press upwardly against the pair of l shaped rocking guides 401 402 whereby the rocking guides are closed completely as shown in fig9 b meanwhile the spreading rod 1 continues to be elevated to bring the small width portion 4 thereof into position within the slit between the pair.