Abstract: The disclosure describes a dual friction clutch, of particular application to motion picture projectors for controlling the operation of spool carrying spindles, in which the drive to a spool can be selectively decoupled, coupled through a weak clutch and coupled through a relatively strong clutch mounted at opposite ends of the spindle, by displacement of a selector device displaceable parallel to the spindle axis to any one of three positions in the first of which the drive is decoupled from the spool, in the second of which the selector connects to the spool through a weak friction clutch and a third position in which the selector transmits the drive to the spool through the strong friction clutch with the weak friction clutch positively locked.

Abstract: The aperture selector mechanism for dual film projectors provides a change-over lever deplaceable between a upper (unlocked) and a depressed (locked) position, resilient means biasing the said lever in the upper (unlocked) position, first deplaceable means cooperable with the change-over lever to releasable lock the lever in the depressed, (locked) position and to release the lever when a super-8 film spool intermediale hub is cooperatively received in the drive spindle of the dual film projector and second deplaceable means preventing the standard 8 film spool intermediale hub to be cooperatively received in the said drive spindle of the dual film projector when the lever is in the upper (unlocked) position.