A carwash brush support structure is extendable relative to a vertical support beam. Extension of the carwash brush carriage is facilitated by means of roller bearings each of which is made up of a U-bolt having threaded ends and a plurality of loosely packed rollers on the U-bolt which engage and roll relative to the surface of a cylindrical rail. The rollers may be of substantially the same size or may be graduated in size toward the opposite ends of the U-bolt to trap the bearing on a cylindrical beam. Rollers of a distinctive color may be located on U-bolt where the greatest roller loading is expected.