Further classifications might be by size. For instance, miniature linear bearings might work well moving a biologic slide sample just a few millimeters beneath a microscope lens while industrial-bearings on injection molding machines carry tooling of several tons. Bushings provide possibly the simplest linear bearing. These thin-walled cylinders can be injection molded of proprietary polymers infused with a lubricant. An oil-infused bronze design, also cylindrical, rides on a polished round rod. This linear-bearing classification is often referred to as slides. http://www.lsyongrun.com/sbr-rail-and-block/