The poly rollers ride on precision ball bearings, they are smooth and well supported. Overall the trolleys are well built with one small exception. The retaining bolt that holds the top rotating pad in place was loose on all four of the trolleys that were received, one was apparently left so loose that all the bearing balls were missing. Still waiting on a response from Vevor as to the remedy. The rubber pads that are supplied to go on top of the rotating portion are useless, they are as thin as paper and thus there is no way to retain them other than glue so you might as well trash them and get something more substantial. Finally the packaging was abhorrent, the trolleys were in a useless bubble wrap baggie and tossed in a box that arrived all busted up and re-taped by UPS.
Jeremy Barron 
