Just about to build a rack for some audio gear, and I'm looking for a suitable rack strip to use.

I noticed that there are rack strips with two or three holes per U. Why is this and which is used for what?

This one has three holes per U: Rack strip with three holes per U

This one has two holes per U: Rack strip with two holes per U

  • I can only guess that it allows you to mount the devices with a bit of distance between them to allow for air flow. Regardless, use what works for you.
    – ghellquist
    Apr 20, 2021 at 17:16
  • Yes, that was also my only guess for why there would be three holes. Maybe that's the reason. Have never seen any equipment with more than two holes per U. Apr 20, 2021 at 17:22

1 Answer 1


Short answer: there are three holes because the specifications require it. Most rack units today have their mounting holes at the corners, but I have seen older multi-RU gear where the holes are placed in what would be the middle hole as well.

The reason two-hole-per-unit strips exist is probably because it works just fine for most gear. Keep in mind that the holes aren't equally spaced between units, so you usually wouldn't be able to move a rack unit one hole up for airflow, this is why you have vented rack panels.

  • To me it wasn't a problem to move the unit one or two holes to leave some air. The cage nuts are quite loose in their cage and also the holes in the gear are oversized. Apr 27, 2021 at 15:34

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