Mini Linear Sliding Guideway 250/300/ 400/500/ 550mm Linear Slide Rail MGN12H Carriage Block for DIY 3 Dimensional Printer and CNC Machine (500mm)

I bought 8 of these. It turns out everybody's reviews are accurate. There's some that are terrible and some that are great. It's a gamble. 2 of them were amazing fits. 1 was a decent fit, 2 were kind of tight, and 3 were too tight. I thought maybe it was preservative gunk, but even after cleaning nothing changed. I could swap and block to the tight ones and they'd always run tight or any block on the good fitting rails and they always fit well. So it's the rails, not the blocks.I bought these because they were offered on a super deal at $11 and I needed more blocks for rails that I already had so figured I'd buy the blocks for $11 and get a free rail. Word of warning, either way, these rails and blocks are out of spec for use with other manufacturers rails or blacks labeled MGN12H. Another manufacturer's depth of cut into the slide was 9.30mm and these ones were about 8.90mm.Would give two stars, but I got them for such a cheap deal that 3 stars is warranted for the value because I'm not sending these back. I'm going to keep them. It ended up being an okay deal for me. The super tight rails I can use on lead screw driven axis and the other 5 are great or decent for belt driven ones. If you're just buying one or two rails it's not worth it because you might end up with all crappy ones and you can buy some other cheap ones from another manufacturer that might cost double but they're still cheap and you end up with what you wanted.

I've ordered 4 of these and received 4 rails made by 4 completely different machines/people/companies.. 1 of them is great, high quality, clean bearings, properly lubricated, and well more than I expected for the price. 2 of them are ok, with some roughness. Both of these needed to be cleaned and lubed properly before use, but are working well and still a good value. 1 of them is hot garbage with mismatched pot metal balls, poorly machined rail, bad wipers, no lube port etc and is now in the trash.I'd return it but I don't know which was which and don't want to penalize the 3 folks that sent me acceptable products..It's really hard to write a consistent review on what are basically 4 different products.

A quick inspection showed the rails had several bearings missing right out of the package and it doesn't even come with spare bearings. An easily fixable issue but still annoying for a brand new part. Did an initial alcohol wipe down & re-lubrication, added the missing bearings but it was still binding. So I checked the carriages and both metal clips securing the bearings were loose due to shoddily designed carriage parts. No wonder the bearings kept popping out. At this point this has already taken an hour of my time, not worth investing any more, its going back. All of my cheapo aliexpress rails are better than this garbage.

This is the worst quality MGN Linear Rail and block that I have ever seen. The block will not even slide on the rail without forcing it. Absolute Junk! Sending back pronto. Stay away.

goods were as described and arrived in a good time frame

3 stars because they work with paired carriage and only pair carriage. Spent way too many hours measuring individual bearing balls to try and rematch a set during cleaning. They also would not accomodate HIWIN carriages. The groove or rail bearing race measured 0.60" shy, allowing the HIWIN carriage to rock. They need a bit of care to clean them initialy but they work well. Just know that these are matched carriage to rail incase you buy multiple. Do not mix them up or clean multiple carriages at a time.

Trash. The springs were bent. (Super crappy ones too). The bearings are like picked and chosen from factory to fit (ie one bearing from one block will bind the other one and the rails would be too tight or too loose.) Mine kept binding. (Maybe adding 3/32 bearings would help but i doubt it). If you want to waste time on these go ahead and buy them

Your browser does not support HTML5 video.  i bought this linear few months ago, the delivery is too long cause of the delay, even tho it came out pretty well packed upon arrived. bearings are good, i put lubricant before instaling and slides smoothly. when everthing is installed i am very happy the results how good quality of my prints. this is the best upgrade that i ever did. so i give it a 5 star

I ordered 2 of these to use together. One worked but not well and the other was seized up. It seems like you need some degree of luck as others haven’t had an issue with these.Would not recommend, There appears to be little to no quality control.

I bought 2 units one really good, the other one was necessary to put some grease to get work, it been a while since I installed them and still working good, I have to add that for 3D print is a good upgrade!