For a SBR Rail and Block or a TBR Rail and Block, there are many linear materials may be needed. Linear bearings are definitely one of them.
Linear bearings generally use a pad, bushing, or roller system to carry a load on a rail that need not be a straight line. The rail can be most any length, although that dimension is limited by the actuator.http://www.lsyongrun.com/tbr-rail-and-block/