American Scale Models trucks do not have ball bearings in the truck side frames, they just use a bronze bearing (bronze is porous so it holds oil well and makes for a good friction type bearing material) which is similar to the style of bearing that Atlas O and Lionel use. The Protocraft trucks have actual ball bearings, similar to the type found in the link below, pressed into the truck side frames and do roll noticeably better than the bronze bearing style trucks. Not to say that the solid bearing trucks don't roll well, because they do roll nice, it is just that the ball bearing trucks still roll better.
Both trucks do have actual external rotating bearing caps, though.
http://www.onlinebearingstore.com/fr-series.html
Scott
