BQLZR Silver Aluminum SHF8 Linear Rod Rail Shaft Support 8mm Linear Motion CNC Router Pack of 2 Each item with our own product label Linear Rail Support A linear reciprocating motion for a variety of mechanical systems, since the role of the support or drive, often with the support shaft, with the use of linear bearings. Inside Diameter:8mm/0.31"(Applicable to the optical axis diameter 8mm)