A rope control device a main body defining a central opening and first and second side portions, projections extending from the main body, an end recess defined by the first and second projections, an end friction surface formed at a juncture of a projection and the main body, and a bar. With the bar in a first position, the first rope portion is extended through the central opening and at least partly around the bar. With the bar in a second position, the main body and the bar define first and second opening portions of the central opening and the first rope portion is extended through the first and second opening portions and at least partly around the bar. The second rope portion is arranged within the first end recess such that, when the rope is under tension, the second rope portion frictionally engages the first end friction surface.

A rope control device a main body defining a central opening and first and second side portions, projections extending from the main body, an end recess defined by the first and second projections, an end friction surface formed at a juncture of a projection and the main body, and a bar. With the bar in a first position, the first rope portion is extended through the central opening and at least partly around the bar. With the bar in a second position, the main body and the bar define first and second opening portions of the central opening and the first rope portion is extended through the first and second opening portions and at least partly around the bar. The second rope portion is arranged within the first end recess such that, when the rope is under tension, the second rope portion frictionally engages the first end friction surface.

A rotary element for a rotary transmission has a helical radial projection disposed about a rotary axis thereof, the helical radial projection having leading and trailing edges of different diameter. A helical peripheral surface between the leading and trailing edges has a radial profile which is inclined to a tangent to the envelope and preferably has an elliptic profile in a radial plane. In use with another such rotary element having a helical radial projection of opposite handedness in a rotary transmission, a point (P) of rolling contact of the helical peripheral surface with a helical peripheral surface of the other such rotary element helically traverses the helical peripheral surfaces of both rotary elements to positively transmit rotary drive between them without interdigitation of their respective helical radial projections and the associated sliding friction between them as arising in a gear transmission.