Abstract: Retention of position and clamping of components is ideally performed with an engagement arrangement which is reconfigurable. Magnetorheological (MR) fluids have been utilised for reconfigurable engagement arrangements but typically require powerful electromagnets to activate the MR fluid. By providing enclosed chambers with a constriction in the form of a passage between a reservoir portion of the chamber and an engagement portion of the chamber it is possible to utilise smaller permanent magnets acting upon a smaller volume of MR fluid in the passage. In such circumstances initial positioning of engagement elements is provided through forced displacement in the form of a plunger or pin and then retention of the engagement element position achieved through positioning a magnetic field across and about a passage to create an effective block retaining MR fluid volume and therefore presentation of the engagement element.