are such that cylindrical pins 11 can freely project from their diametrical borings 8 into the adjoining sections of longitudinal boring 7 but the arresting balls 10 can enter only the funnel shaped portion 22 of the rotary members 9 the end of plug 2 facing the rear cover plate 13 is provided with a radial extension 3 which projects through a recess 23 in sleeve 1 into an axially directed groove 4 in the inner wall of housing 5 this axial groove 4 communicates with an annular groove 6 provided in the inner wall portion of housing 5 for guiding the extension 3 so that this extension together with plug 2 and sleeve 1 can be rotated by key 19 about a common center axis this rotary movement however is possible only in the position of plug 2 in which the diametrical borings 8 of rotary members 9 are aligned with longitudinal boring 7 and plug 2 is axially displaced to the right as illustrated in fig1 if plug 2 is shifted to the left the extension 3 is out of alignment with annular groove 6 and axial groove 4 prevents the rotation of the plug a pressure spring 14 arranged in a central opening of terminal plate 13 urges a spring pin 24 against the center of the base of plug 2 and pushes the latter to the left to facilitate the movement of plug 2 in sleeve 1 a jacket 25 is interposed between the plug and the sleeve the jacket reduces friction between the plug and the sleeve and also supports pivot points of rotary members 9 in the inoperative or arresting position of plug 2 in which no.