Abstract: A wheel is partly closed at one side by a hub cap (1) continuous with the rim (6) and is designed to receive an axle from the opposite side. According to the invention, the hub of the wheel consists of a plurality of ribs (14-17) which serve as bearing faces for the axle and whose geometric, axial elongations clear a plurality of spokes (2-5) forming the connection of the hub cap to the rim (6). This enables injection moulding in one operation with the simultaneous provision of an inside cavity behind the hub cap to receive a radially resilient and projecting bead (11) at the end of the axle.

Abstract: A fluid-pressure-operable device 1 includes two relatively-movable components 2, 3 defining a variable-volume working chamber 9. A sealing element 5 of elastomeric material is carried, or formed, by one of the components and is in sliding and sealing engagement with the other of the components normally to resist escape of fluid under pressure from chamber 9 to the exterior thereof. That face 15 of element 5 remote from the chamber is so provided with channel 16 that as pressure in the chamber increases the element is permitted progressively to deform and some of the material of the element thus displaced is then accommodated by the channel. When the pressure exceeds a predetermined value, deformation of the element is such that sealing engagement of the element with the other of said components is broken so that the pressure in chamber 9 is relieved to the exterior thereof.