Genuine ZYLtech MGN12 linear and MGN12H long carriage block are both real grade C with the following details:
- Precision grade C grounded and polished
- Interchangeable bearing blocks/slider carriage for versatile configuration
- Dimensional tolerance of height H and width N: +/- 40microns
- Maximum travel distance error: +/- 17 microns per 300mm and +/- 23 per 1000mm
MGN12 rail ⌀3.5mm mounting hole spacing is 25mm
MGN12H longcarriage block size 27x45mm, M3 mounting hole spacing 20x20mm
The listing is for one rail plus one or two carriage blocks . For light duty applications(such as laser engraver or 3D printer) , it's acceptable to use one rail per one axis. It's most common to use two rail and two carriage blocks per rail for one axis.