MGN12 300mm Linear Rail Guide with MGN12H Stainless Steel Carriage Block - Compatible with Ender 3, Corexy, Tronxy, Delta Kossel 3D Printers & CNC Machines - Precision Upgrade for Smooth Motion & Enhanced Printing Quality - Perfect for DIY 3D Printer Modifications and CNC Router Builds

These rails really perform pretty amazingly right out of the box. Unlike a lot of the cheaper Hiwin replicas out there, these came nicely oiled and sliding smoothly instead of covered in shipping wax and dragging.That being said, I still did my standard practice of disassembling the rails, cleaning with isopropyl alcohol and re-lubricating with Slick50 Supercharged One Lube and MAN are these things smooth now!While I had them apart, I noticed a few small details that I think are major contributors to these rails performing better than most. First, the quality of the molded plastic parts is much better than expected. There is no flash on any of the edges and they all fit together nicely. Second, and maybe more importantly, the start and end of the tracks that the balls actually roll in have been carefully relieved and tapered so that when the balls enter and exit the tracks there is no hard edge to roll ever and cause any clicking or dragging.These rails are FAR better quality than the offerings of RobotDigg and blow v-slot wheels rolling in 2020 aluminum extrusions out of the water. In my case, an Ultibots D300VS+ delta printer, the swap from v-slot wheels to these linear bearings cause the result of a vase mode test print to go from the ripply appearance of the blue part pictured to the buttery smooth appearance of the black part using the same g-code!Long story short, these are pretty great rails in my experience. Give them a shot!