19-inch rack Structural support
Rack-mountable equipment is traditionally mounted by bolting or clipping its front panel
to the rack. Within the IT industry, it's common for network/communications equipment to
have multiple mounting positions, including table-top and wall mounting, so rack mountable 
equipment will often feature L-brackets that must be screwed or bolted to the equipment prior 
to mounting in a 19-inch rack. With the prevalence of 23-inch racks in the Telecoms industry, 
the same practice is also common, but with equipment having 19-inch and 23-inch brackets
available, enabling them to be mounted in existing racks.