The coupling 10 has a disc spring 16 between a plate 12 with an aperture 22, a second member 14 with a hole 34, a connecter 20 passes through the holes to maintain alignment of the plates when they are moved relative to each other. Preferably the disk spring 16 is a stack of five Belleville washers 18 arranged in alternating series, which is partially housed in a cavity (fig.2,24) of the plate, and sits on the second member. The second member may have a slot 36 for attaching a displacement measurement device such as a linear potentiometer. The connector may be a bar with a base plate 44 and a removable lock member 50 to prevent axial decoupling. The coupling may form part of a load cell in a motorised patient hoist (fig.4,100), located between an adaptor plate (fig.4,166) of a rail bogie (fig.4,164) and the carriage body (fig.4,158)； or a load cell may be provided for each leg of a bed frame. A method of determining a load by measuring displacement is also claimed.
