Linear Bearing for 5/16 inch round chrome plated rod.

thingiverse

This linear bearing was engineered specifically for a 5/16 inch chrome-plated rod. Some local hardware stores may carry smooth chrome-plated rods over short distances, but PLA is a stiff plastic that can glide effectively along these rods. The stepper motors used in three-dimensional printing possess sufficient torque to pull linear bearings on a chrome-plated rod back and forth even though frictional forces are higher than when using a rolling linear bearing on a hardened polished rod shaft. If the load on the bearings is light enough, you may be able to use a linear bearing printed in PLA instead of investing in more expensive linear bearings like LM8UU's or polished hardened 8mm rod shafts. You can also try printing linear bearings in other types of plastic such as nylon, which should have a lower coefficient of friction when sliding on metal surfaces. This part was designed using the freeware version of eMachineShop.