PLEASE NOTE only available as a separate purchase. The Joist Proppa can be converted into a trolley for moving heavy doors and/or window frames, by attaching the outrigger castor set. The two (2) EVA sanding blocks included in the Joist Proppa set can also be used as wedges to protect against marking by the spikes and washer when the Joist Proppa is in its trolley mode. Maintain constant and appropriate manual control over the Joist Proppa when in trolley mode.