This is a bit of a ramble with a TLDR of "I would prefer to work solely in metric." The eccentric spacers from the OB store (and any other store I could find them at) are a mixture of metric and US. The I.D. is set for M5 screws and the length is 1/4". I cannot find M5x8mmx0.25" concentric spacers, they don't seem to exist unless maybe you can have them custom made ($$$). This would be partially ok if not for the cheap spacers the OB store has been using (no offence Mark). The I.D. of those spacers is much too large (7mm) and material is much too thin (0.5mm). This is causing my bearing bolts to skew just slightly when tightened. This in turn makes the bearing too tight or too loose depending on how the spacer is sitting. The eccentrics are only designed to tighten the carriage to the rail, not make up for mis-aligned bearings. If the spacers were the correct M5x8mm spacers, you'd have an I.D. of 5.0-5.2mm and an O.D. of 8mm with a material thickness of 1.4-1.5mm. Even better if we used M5x10mm spacers as then you get a solid 2.4-2.5mm material thickness and the spacer becomes much more stable. Of course, this again comes back around to the fact that the length we need is 1/4" due to the eccentrics using a mixture of sizes. So, since we have this mixture I thought maybe I would try to find a way to normalize the eccentrics to metric lengths. 1/4" in metric is 6.35mm and my idea was to find a M5x1.35mm shim but I've been unable to source that part. Since I cannot source a shim to normalize the eccentric spacer, the other option would be to source metric only eccentric spacers. I cannot seem to find those either, at least no in the sizes we need. My current solution is to loosen all the bolts, assemble the pieces and slowly tighten them back working top down in an attempt to let the weight pull them all into the same alignment. I've yet to get it perfect but it's a little better. If there is a better way, please let me know. Perhaps I'm totally misguided on the spacer issue causing the bearings to be misaligned. Please tell me if I am. Even if I am misguided there, the mismatch of US spacers on an otherwise metric machine cause another issue, at least on the OX. The Y carriage uses a 65mm bolt with 2 wheels to span the double width Y beam. The spacing of the slots is 100% metric, but it's impossible to get the wheel spacing correct using a US spacer and metric shims. You can get close, but if you look at where the wheels ride, they are not correct. The slot centers are 20mm apart, the wheel center to outer edge is 5.5mm. That's 20 - 5.5 - 5.5 = 9. You need exactly 9mm between the bearings on each wheel. Using a 1mm shim on each side you need a 7mm spacer, not a 1/4" spacer (6.35mm). Frustrating, but solvable by finding an M5x8mmx7mm spacer at another shop. I love working with the OB v-slot rail, but I wish that all the parts were 100% metric. Comments and suggestions are greatly welcome.