Well I got my name brand HIWIN guides. 2 545mm rails and 4 sliding blocks. mgn12h. And all I can say is wow. They have drag on them. There is preload. but they are so damn smooth. The rails come all oily. and each block is individually seaked in a blister pack and they are also really oily. The rails are etched with HIWIN logo as with the blocks. And they are just so incredible that it hurts me to realize that I now must backup and replace the other Chinese B.S. I have already on my frame for X and Z. This is my first experience with the linear guides and what I have learned is that it pays to spend the money on the name brand high quality parts. HIWIN from Motion Constrained and you will be impressed. From Ebay and may God have mercy on your printer's soul. I wasted a chunk of money learning this lesson.