100% tool-less PTFE bearings that pop into place with a firm push.
They can be arranged in line with the rail, or horizontally. They can be solid, hollow, or semi-hollow. They can hold lubricants (under pressure if need be), and dyes (for discovery of service failure). They can even be ran in a spiral pattern and have coolant ran through them. One 1/4" insert costs less than one penny, and slides, or pops right into place. Solid state bearings are nothing new, but they have never been this cheap or easy to work with.
I would recommend using solid PTFE for high wear applications, like 3d printers and CNC routers. The more inserts you utilize, the less deflection you will get. It would be really cool to see this used in metal if anybody with those capabilities is game. I've got a CNC router kit, but it's currently in a million pieces. More to come!
Each insert is held in place because at least 50% of the insert/inset is recessed within the housing. Hollow PTFE is able to act as a damper, and fluidic dispenser. This also works with nylon, PEEK, phenolics, acetal (Delrin), UHMWPE, Polyimide, polysulfone, and polyphenylene sulfide. A round profile was chosen for the bearings because it is widely manufactured, cheap, and because of it's shape, able to be retained in place without fasteners.