Bar 1 slides in fixed guides a-a. Spring 4 is arranged between two washers 5 which slide freely along the middle part of bar 1 and are held by the spring against shoulders. Slider 2, moving freely along bar 1, has two bevels b. Pin 3, spring-loaded by spring 6, slides in fixed guides c and, engaging bevels b, indexes slider 2 in its ext reme positions. When bar 1 is shifted to its other extreme position, spring 4, overcoming the resistance of pin 3, shifts slider 2 in the same direction to its other extreme position.
$2135$EL,SE$