rack rails

[DaveySimps]

Hardware for mounting of equipment in a permanent or portable enclosure.

http://audiopile.net/products/Cases/EWI_Case_Hardware/RACK_RAILS/EWI_Rack_Rail_cutsheet.shtml

EIA-310 specifies 18.312" from center of hole to center of hole [horizontally] on the rails and a minimum 17.72" clear dimension inside the rails and those are the dimensions that really matter. The 19" in the standard relates to the equipment front panel width, not the clear rack width, and to allow for clearances most racks have a slightly greater than 19" clear width.

Vertically, holes are spaced for gear height in 1.75" increments.

Rack ears: Metal tabs or extensions to the housing of a device that allow it to be mounted with screws in a standard 19" equipment rack.