I fitted some heavy duty castors to an old Laney 4x10, mainly so I could shift it around rehearsal rooms and once you're inside venues. But my mate decided to push it, rather quickly, along an uneven pavement. All I heard was a loud banging and turned around to see the cab sliding along the ground as my mate fell over the 4 castor he'd sheared off the bottom. The base plates are still on the bottom of the cab mind...