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We have just purchased a APC rack (model AR204A) with 12-24 threaded holes. We couldn't get a "square hole" model in time for our setup deadline. Unfortunately our rack servers (Lenovo RD240) appear to have 10-32 thumbscrews for securing the server to the rack. We've successfully mounted the server rails to the rack using 12-24 screws however the 10-32 thumbscrews in the server front won't "grab" the 12-24 holes in the rack, thus there is nothing to stop the server from sliding right off the rack if pushed from the back.

The thumb screws on the server don't seem to be removable, so we can't simply use 12-24 screws instead. Any suggestions on how to work around this problem? Is there any way to "convert" a 12-24 hole to a 10-32 thread (or similar approach)?

Thanks in advance.

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The only way I know of to put a smaller screw in the hole is to use a Helicoil. Though I wouldn't really recommend it, sounds like your in rough shape... –  Chris S Jun 4 '12 at 13:41
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Not to sound pithy, but is there really a danger of pushing the server out of the rack? Who is it that would be pushing the server out of the rack and when might this occur? Presumably the server is "locked" into the rails and the rails can't be pushed out of the rack seeing as they've been secured to the rack, so how would this come about that the server could get pushed out? –  joeqwerty Jun 4 '12 at 14:40
    
@joeqwerty - I think the OP is just being thorough and not wanting it to give/slide at all while working behind the server. There doesn't appear to be any danger of the server falling since it is on rails as he states. Unless I'm reading his post incorrectly?? –  TheCleaner Jun 4 '12 at 15:48
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@joeqwerty EaRtHqUaKeS? –  voretaq7 Jun 4 '12 at 15:54
    
I get it. My point being that if the server is secured to the rails and the rails are secured to the rack... how could the server be pushed out of the rack? If an earthquake is able to knock the server out of the rack it has to do so by knocking the secured rails out of the rack, in which case, having the server secured to the rack probably provides no additional protection against such an event. Again, not trying to be pithy, just trying to determine the probability versus the possibility. –  joeqwerty Jun 4 '12 at 16:05
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3 Answers

up vote 4 down vote accepted

I think anything you do will require modifying the rack. 12-24 is larger than 10-32, so you can't drill out to that size.

You can drill out to a square hole and add an insert.

You can make use of a helicoil that will allow you to drill out the 12-24 and get an effectively smaller 10-32 hole. Things like this are presently available on Amazon or your local hardware store.

Bribing your local car mechanic to give you a hand is a solid idea for this. They've almost certainly had to place a few in their career.

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Thanks, drilling out to make a square hole is a great suggestion. Then we can use the proper cage nuts to match the server. Going to investigate that option! –  JJ. Jun 4 '12 at 17:50
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My suggestion is cheapo, but will do the trick. Don't laugh.

Go to Lowe's/Home Depot and pick up heavy duty double sided velcro tape. Cut the strips narrow to size and then stick them on the rails and server front so that when you push the server into the rack the velcro catches.

This way it takes some effort to pull the server from the rack.

Just to clarify the above. My answer is based on the OP stating he only needed a way to prevent the server from sliding out of the rack if pushed from the back.

As stated by the OP:

We've successfully mounted the server rails to the rack using 12-24 screws however the 10-32 thumbscrews in the server front won't "grab" the 12-24 holes in the rack, thus there is nothing to stop the server from sliding right off the rack if pushed from the back.

Effective... for a server that's on rails, anyway. Velcro has great holding strength at sheer (pull being parallel to the Velcro), but is lousy under an angle or leverage. If your server pivots, it's going to fall in a way that a screw would prevent. So, use it if you're just holding the server to the rack when the weight is already supported. Don't use it to hold something like a switch.

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Decided I rather edit my caveat in and +1 you... –  Jeff Ferland Jun 4 '12 at 14:48
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I would certainly trust the velcro to hold a server. I would certainly NOT trust the adhesive on even industrial velcro to cling to metal/paint well enough to not come loose - particularly in the back where server exhaust can reach hair-dryer temperatures and melt the glue off... –  voretaq7 Jun 4 '12 at 15:19
    
@JeffFerland - yeah my answer was based on the OP stating that he had racked the server but just needed a way to keep it from sliding forward out of the rack if pushed/nudged in the back. –  TheCleaner Jun 4 '12 at 15:44
    
@voretaq7 - there wouldn't be velcro tape on the back. Read my comments and edits –  TheCleaner Jun 4 '12 at 15:46
    
@TheCleaner That's more sensible I object to using velcro as a retainer too, but substantially less than using it as a structural component :-) –  voretaq7 Jun 4 '12 at 15:49
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You should have purchased a proper square-hole rack enclosure/frame. It would be a better move long-term as threaded-hole racks are not ideal for mounting servers. Square-holes + cage nuts are more flexible and can accommodate more equipment types.

As for the screws on the server's front bezel/faceplate, chances are that they are meant to mount to the front edge of the rail in a standard square-hole installation. Depending on how you mounted the rail kit to the threaded-hole rack, this may not be possible.

Edit:

Looking at the installation guide for the rail kit included with the Lenovo server, you would have needed to modify the pins at the front and rear of the rail arms in order to accommodate the threaded holes in your rack. Referencing the image below, you'd remove #1 and #2, leaving a flush surface to mount the rail ears to your rack. The small threaded hole in between #1 and #2 is meant for the captive thumbscrews on the front bezel of your server. That's how the server should stay secured to the rails/rack. I think it depends on you using a flatter-head screw to secure the rail kit to the rack's vertical rails, but the thumbscrew should be able to reach.

enter image description here

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Thanks for the input, but as I stated in the original post, this wasn't possible. We had a very tight implementation deadline and no rack model with square holes could be delivered to our location in time. –  JJ. Jun 4 '12 at 17:27
    
Understood, but once installed, you'll have a difficult time moving to a different rack. Either way, I wouldn't be too concerned about pushing the server out of the rack unless it's not level. This isn't a big deal. –  ewwhite Jun 4 '12 at 17:29
    
It is a big deal actually. Maybe not in your environment but in this case yes there is a risk of it being pushed out by accident. –  JJ. Jun 4 '12 at 17:53
    
See my edits. You should be able to secure things this way. –  ewwhite Jun 4 '12 at 19:05
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