Fits Perfectly in 3D Printer Pillow Block. these only work if your rods are straight, If rods are bent, they lock up and don't work correctly. These slowly release lubrication as they slide,and using additional lubrication will decrease the life and could cause performance issues. Item Type: Ball Bearings el Number: RJMP-01-08 Inner Diameter: 8mm Outer Diameter: 16mm Length: 25mm Usage: 3D Printer Part colour:yellow Material:Engineering plastics Package Contents: 10 * bearingOnly the above package content, other products are not included. Note: Light shooting and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.