Square Mounting Holes Sold In Pairs Black Powder Coated Steel Our "Z" Series Steel Rack Rails have 3/8" square holes on both front and side facing legs. Attachment holes for securing into a cabinet or enclosure are 9/32" diameter. A convenient etch mark is plainly visible every rack unit (1-3/4") along the full length of the rails. 3/8" square mounting holes are spaced per the EIA 1-3/4" rack unit standard. Rails are sold as a set of 2. If you need additional rack rails to retrofit into rack cases, rack enclosures, rack cabinets, or custom installations, you'll want to consider one of our 3 other Multi-Application Rack Rails.