Abstract: An earplug for use by an underwater diver includes a tubular vessel of soft flexible material adapted for insertion into the auditory meatus, a plurality of sealing rings surrounding the vessel to seat against the interior surface of the auditory meatus to provide a watertight seal, and a flexible inner vessel end inwardly rolled back upon itself to define a variable volume between the inner end, the interior surface of the auditory meatus, and the eardrum. The variable volume expands and contracts as the diver ascends or descends to maintain pressure equalization across the eardrum, yet prevent the entry of water into the auditory meatus. If the eardrum should rupture, the inner end of the vessel flexes to its full extent but still prevents the entry of water into the middle and inner ear regions.

Abstract: A tow cart is provided with an arrangement in which the tow or drive pin is adapted to be moved out of engagement with the conveyor drive, in response to a predetermined degree of obstruction to the tow cart, by a spring-loaded overcenter double toggle movable from a cocked to a released position in response to the obstruction, and in which the drive pin is pivotally supported so that it may swing forwardly away from the conveyor drive upon the release. In the cocked position of the toggle mechanism the mechanism restrains the forward pivotal movement of the drive pin.