From the research I've done, the rack rail market seems to be very brand-centric. It's really hard to be sure that the rails I buy will match the servers as well as the rack. I'm in a position where I have rails that match the rack but not the servers, and rails that match the servers but not the rack.

From what I see, the main difference between the brands is the location of the screw holes for the inner part of the sliding mechanism. My question is two-fold:

  1. Is there a diagram that shows across all brands what terms are used when specifying rail types and dimensions, options for "slotting", etc., but particularly depth (so that they reach the back post) and screw hole placement to match the servers?
  2. Are there generic nU telescopic rail kits that would work on most nU servers regardless of brand?

Back story

I've been handed a bunch of 1RU IBM x3250 M2s, and I have to mount them into a 19" 4-post rack which is 29 inches deep with square holes. Unfortunately, I only have one pair of rails, and they don't seem to extend quite to my rack depth of 29 inches. They're short by maybe 0.75". I've tried inserting "rail extensions" (long bolts) in, but there are other issues...

The rails with the x3250s are basically two tiny shelves (one on each rail) half the length of the server which, when fully extended, seem only barely to support the units and aren't very stable since all the weight causes the rail to rotate. When fully extended, there appear small gaps which, if the angle of the server is not perfect as its pushed in, the server falls through. (Yikes!)

The rails I have from some newer Intel servers are sliding rails, and these I prefer since the servers can't fall out without lifting them or activating the release mechanism. However, the screw holes don't match. Before I go drilling holes in newer rails, I want to check that I'm using the right terminology when searching for rail kits.

  • 1
    What type of rack do you have?
    – ewwhite
    Aug 4, 2014 at 11:35
  • The short answer is I don't know. It was handed to me when I requested we purchase a rack because our current ones wouldn't fit the depth of the newer servers. How do you tell? Aug 4, 2014 at 23:26
  • 2
    I'd look for a model, product label, manufacturer information or take a photo.
    – ewwhite
    Aug 4, 2014 at 23:28
  • You can usually adjust the depth of the rack. All of the vertical square hole posts adjust front to back.
    – dmourati
    Aug 5, 2014 at 4:48
  • @dmourati Unfortunately in this case the rack depth is determined by the fixed-size shelves. Aug 6, 2014 at 1:12

2 Answers 2


First, please take a look at: What to look for in a server rack?

These days, racks are pretty compatible and server rails solutions to accommodate 4-post square-hole racks are flexible.

A mistake people make with some rack enclosures is not adjusting the depth (if adjustable) before mounting their gear. If I'm building out a new co-location site using adjustable rack depth, it's the first thing I modify.

When it comes to your specific hardware's rail kits, make sure you're using them correctly. If unsure, pull the online instructions/documentation for the server and check the implementation guidelines. Your comment on "screw holes" not matching probably means that the rails are of the "tool-less" type and aren't meant to be screwed in. Also double-check your rack-unit enumeration (the holes are NOT equally spaced). As for the fixed-rails on the IBM x3250 M2, they are not telescoping rails. You're not supposed to be able to extend the server with them. It's just a shelf.

So there are two issues. If using a non-IBM rack, there are clipnuts/cagenuts that you'll need in order to prevent the twisting you mentioned. If you find that the stock rail kits for the servers you have are just not suitable, you can just go 3rd party... I would suggest using the specific x3250 M2 kit from Racksolutions.

  • Thanks! Telescoping is a term I hadn't come across. Unfortunately, the depth is fixed by fixed shelves that are exactly 29" deep. I had considered throwing these out so that I could reduce the depth, but I'd have to balance that against the cost of new rails, etc. Aug 4, 2014 at 23:25
  • @tudor I provided a link to universal adjustable rails that could be used with your server.
    – ewwhite
    Aug 4, 2014 at 23:27
  • Thanks again! I had seen these, but they appear to be non-telescoping. They also seem a bit expensive for non-telescoping rails, no? Aug 4, 2014 at 23:29
  • @tudor You don't need telescoping rails for the type of server you're talking about. See this post to understand why. IBM make a telescoping rail kit for that server (parts #46C7860 and #46C7861), but it's really not worth it. Find them on eBay. These are old servers, though...
    – ewwhite
    Aug 4, 2014 at 23:33
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    Oh, and by the way, as much as I respect and appreciate you investing in my specific difficulty, it doesn't really answer the question(s) which were more knowledge-based. My question was to do with standardised terminology in racks and rails, and you've now partially answered the second question (by implication) but only in the comments. I was expecting more of an answer defining terms. I'll change my bolding to emphasise this. Aug 5, 2014 at 0:56

Server rails are entirely proprietary and often vary from model to model. Rack depth is also variable although in most racks you can reposition the posts to change it.

The other thing you could use are generic rack shelves.

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