An encoder device (5, 6), comprising: a housing; a hub rotatably arranged in the housing and arranged to carry an encoder disc; a cover (30, 31) that is axially movable between a first position and a second position; and a gapping and centring device including a plurality of clamping elements arranged to urge the hub into a predetermined axial and radial position relative to a portion of the housing when the cover (30, 31) is in the first position, the gapping and centring device arranged to permit axial and radial movement of the hub when the cover (30, 31) is in the second position, the actuation of the gapping and centring device causing the clamping elements to move radially outwardly to remove the clamping force applied to the hub; wherein each clamping element includes at least one projection that extends radially inwardly into a circumferential groove of the hub when the cover (30, 31) is in the first position each of the clamping elements is mounted on at least one spring arm configured to exert a radially directed force onto the respective clamping element; wherein the spring arm is arranged to apply a radially outwardly directed force on the respective clamping element when the cover (30, 31) is in the first position; wherein each of the clamping elements has an actuation member that extends radially outwardly and is arranged to slidably communicate with the cover (30, 31) to translate axial movement of the cover (30, 31) into radial movement of the clamping elements, thereby drawing the clamping elements out of the circumferential groove and radially outwardly away from the hub when the cover is moved to the second position. a housing; a hub rotatably arranged in the housing and arranged to carry an encoder disc; a cover (30, 31) that is axially movable between a first position and a second position; and a gapping and centring device including a plurality of clamping elements arranged to urge the hub into a predetermined axial and radial position relative to a portion of the housing when the cover (30, 31) is in the first position, the gapping and centring device arranged to permit axial and radial movement of the hub when the cover (30, 31) is in the second position, the actuation of the gapping and centring device causing the clamping elements to move radially outwardly to remove the clamping force applied to the hub; wherein each clamping element includes at least one projection that extends radially inwardly into a circumferential groove of the hub when the cover (30, 31) is in the first position each of the clamping elements is mounted on at least one spring arm configured to exert a radially directed force onto the respective clamping element; each clamping element includes at least one projection that extends radially inwardly into a circumferential groove of the hub when the cover (30, 31) is in the first position each of the clamping elements is mounted on at least one spring arm configured to exert a radially directed force onto the respective clamping element; wherein the spring arm is arranged to apply a radially outwardly directed force on the respective clamping element when the cover (30, 31) is in the first position; wherein each of the clamping elements has an actuation member that extends radially outwardly and is arranged to slidably communicate with the cover (30, 31) to translate axial movement of the cover (30, 31) into radial movement of the clamping elements, thereby drawing the clamping elements out of the circumferential groove and radially outwardly away from the hub when the cover is moved to the second position.