I am using eccentric spacer nuts to create a tight fit between wheels and a rail of a linear sliding mechanism. (Expand the product description in the link to see a picture of it in use).

They aren't actually nuts: they have no thread. But the hexagonal part of its exterior allows the spacer's off-centre hole to be adjusted with respect to the external cylindrical section with a spanner, thereby positioning a shaft going through it relative to the structure holding them.

Are there alternative mechanisms for adjusting the distance between opposite wheels? They are very effective, but are £2 per piece from the UK, and it really adds up. They only seem to be sold by suppliers of the open-rail and v-slot systems, so I'm hoping, either:

  1. These accent rich spacer nuts are known as something else in other systems, at a lower price, or...
  2. There are other mechanisms that achieve the same.
  • $\begingroup$ Alternative mechanism for adjusting the distance between opposite wheel: I believe they are called slots. :-) Seriously, one set of wheel shafts could have been placed in slots with precision shoulder screws acting as the shafts. This will be a no-brainer to give you adjustment in two planes, up and down with shim spacers under the head of the shoulder screw and of course side to side inside the slot. $\endgroup$ Commented May 7, 2016 at 21:10
  • $\begingroup$ Fair point! But gives less fine control over the adjustment, tightening can change the position, and the position is more prone to slipping $\endgroup$
    – Jodes
    Commented May 7, 2016 at 22:44
  • $\begingroup$ Fair points! One trick to solve all three problems. Slide the wheel assembly over so the wheels kiss the rails. In this position freeze the wheel assemble in place with a nest, some metal bars that you just tack around the wheel assembly with a little super glue to capture it on the carriage . The bars should be pre-drilled with thru holes for screws and maybe some dowel pins so you can secure this nest to the carriage. Now you can hog down your mounting nuts without fear that the wheel assembly will shift or slip . I have used this super glue trick for many types of assemblies , it works. $\endgroup$ Commented May 8, 2016 at 0:55
  • $\begingroup$ No offence, but if you think what I just described to you is "Rube-Goldberg-ish", me-thinks maybe engineering is the wrong field of endeavor for you. $\endgroup$ Commented May 8, 2016 at 15:10
  • $\begingroup$ If these eccentric spacer nuts don't have a thread, what's stopping them from turning under a load? Especially if the "correct" position is 90 degrees from either of the extremes, the shaft and the wheel seem to apply a significant moment on them... $\endgroup$
    – SF.
    Commented Sep 18, 2018 at 10:46

1 Answer 1


Try this post from CNC Zone, where an explanation is given on making your own eccentric spacers.


  • $\begingroup$ Welcome to Engineering! So as to avoid link-rot, please expand your answer to include the relevant information from the link provided, at least the most essential points. Feel free to quote directly from the source. $\endgroup$
    – Wasabi
    Commented Sep 18, 2018 at 13:40

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