Abstract: A trolley has rear support wheels (20) each having a toggle (52) which, when in a cocked position, hold the wheels in an operative position in which they are able to support the trolley. When the trolley ceases to bear down on the rear wheels, for example when an attempt is made to lift the trolley over a barrier (26) along the periphery of a defined area from which the trolley is not supposed to be removed, the toggle is triggered to move to an un-cocked position. When the toggle is in the un-cocked position the support wheels collapse and are no longer able to support the trolley. This will discourage removal of the trolley from the defined area.

Abstract: Wheel assemblies for attachment to a carriage or a vehicle. The wheel assemblies can be configured for four wheel steering, locked in predetermined directions, or free pivoting. The wheel assemblies further include an apparatus for retracting and extending the wheels of the carriage to support the carriage on fixed length supports.