The present invention relates to metrological rotary devices, such as anemometers and the like. Specifically, the present invention relates to a mechanical coupling for the same, whereby an anemometer cup-rotor or like device, can be replaced without the use of a tool. The present invention seeks to provide a coupling device which makes a mechanical coupling between a first and a second member such that the locking together and release action is positive, without likelihood of failure, and can be conducted simply and quickly without the use of a tool. Further objects of the invention are to provide couplings in which a positive axial and rotational location of shaft as first member and mating bore in a second member are obtained which do not cause damage to either of the sliding surfaces when excessive force is applied, and which are capable of transmitting a torque, such couplings being suitable for attaching a rotor to an anemometer. In particular, the present invention provides a coupling arrangement for an anemometer rotating body comprising impellor cups, which impellor cups and rotating body are required for removable fitment, ideally without the use of tools.