CamonWheels is offering up some new V-Groove roller wheels for under $8 bucks shipped. Images show the grooved wheels fitting on 15mm rods, 1/4" rod, and 1" PVC. The overall OD of the wheel (outside diameter) is at 1". If you were to build a track dolly of sorts, the V-Groove or U-groove type wheels will help keep them on track.

CamonWheels Video Dolly DIY Wheel Set