On Thursday, March 31, 2011 02:40:32 am John R Pierce wrote: > oh, see http://www.server-racks.com/rack-hole-types.html for a bit more > about this, along with links to summaries of the various maker's rail > systems And, if you can find a copy, see EIA RS-310-C "Racks, Panels, and Associated Equipment" and/or IEC 297. EMC 40U racks are unthreaded round hole, universal pattern. And most of my threaded-hole racks are 10-32; I only have a few two-post aluminum racks that are 12-24. EMC's rail kits use 10-32 threaded inserts in the rails, too. How does this relate to CentOS? Well, CentOS sees use in lots of servers, and servers are typically in racks, and the last I looked there were no 'rack hardware questions' mailing-list...... :-) But, yeah, OT.