A coupler device for coupling an attachment to a mechanical arm of a machine or vehicle, comprising a main hitch body (2), an actuator (3) mounted to the main hitch body (2) and moveable relative to the main hitch body (2) and a front locking mechanism. The front locking mechanism comprises a first locking member (4) adapted to be pivoted by operation of the actuator (3) from an open position to a closed position to engage with a first pin or other means of an attachment to secure the attachment to the mechanical arm and a second locking member (6) provided on the main hitch body which is adapted to mount the actuator to the main hitch body when the first locking member is in its closed position such that the main hitch body prevents the first locking member (4) from pivoting into its open position.