There are 3 main builders of pizza box format servers (19" - 1U, 2U…):
They all three sell their own rails for the standard or proprietary bay to mount their devices in racks.
But what are the differences between them?
Is it possible to use Dell rails on IBM server?
Is it a question of holes position? Or something else…
I have found this FAQ, but it doesn't gave me answers: https://www.server-racks.com/
What if I buy another brand like Cisco, Apple, SuperMicro or whatever?
Rackmount servers come with rails intended for that equipment. The rails are generally unique to the server model and manufacturer.
It IS possible to buy generic universal rails, but there isn't a reason to since obtaining the right rails for a particular server isn't difficult.
In my experience, it's not possible to use rack mounts from different vendors on different machines.
There may be some system where where generic cases are used, and thus, generic rails are available.
My answer to the question "Can you use Dell rails on a IBM Server?" No, you can't.
The server/system manufacturer supplies the rails that fit to their equipment. There is no universal standard in that regard.
Rail kits from one product line may not even fit another product line from the same vendor and mixing and matching between different manufacturers is even more unlikely to work/fit.
Fortunately 19'' cabinets are a universal standard and you should usually be able to fit railkits from different vendors in the same cabinet, with some minor considerations when you order them:
19'' cabinets can vary in depth, and not every railkit is (fully) adjustable.
Some rail-kits or mounting sets can come in two-post and four-post flavours, with the four post cabinet the usual type for server cabinets and two-post the more traditional standard for wiring cabinets used by telco's.
And then posts in your cabinet can also come with different hole types:
and you may for instance need to bring the correct cage-nuts
