Abstract: A detector head can assume two positions selectively on a mount which is in turn fixed with adjustable orientation on the cover of the casing. Two and the same perpendicular channels in the head, and two and the same perpendicular tapped holes in the mount are occupied by two screws fixing the head on the mount in the two positions of the head on the mount. The channels extend along two edges of the head without obstructing the space available inside. They converge towards an edge along which the mount extends in a very compact form. The two perpendicular screws provide a strong and compact connection between the head and the mount.

Abstract: A reciprocal locking device for the movements of two push buttons includes a pivoting bolt having the shape of a "T" which oscillates in a plane perpendicular to the directions of displacement of the push buttons and is urged back into a central rest position by its own resilient means.

Abstract: An electrical switch apparatus has a pair of first switches and a second switch each with a spring-loaded part for actuating its contacts. The switches are arranged in a casing in which two slides are movable against springloading in convergent paths. Each slide has first and second cams to engage with and move the actuators of a respective first switch and the second switch, the arrangement being such that when one slide has commenced to move in the switch-actuating direction, it blocks the path of the other slide, with the result that each slide can be moved to actuate a respective first switch and thereafter the second switch, but it is impossible for both of the first switches to be actuated at the same time.