The Liberator Fourth Wheel Attachment takes the load bearing responsibility off the operator and puts it on the hand truck. This extra set of wheels secures easily to the back of the frame on 2 wheel hand trucks that are not convertible and do not ha ve stairclimbers already attached. Many hand trucks have holes pre-drilled for the installation of accessories like this. If your hand truck does not have holes you may be able to drill them yourself.When the hand truck is tipped back these extra cas ters support the load instead of making the operator support it. This accessory is a must for the frequent transport of heavy loads