Cantilever racking is based around a central upright, which could be a standard structural steel section, attached to a base section.  The arms are either bolted to the upright on a pre determined pitch of say 100 - 150mm depending upon the design required or can be infinately adjustable by the use of clamp plates.

The arms can be either fixed to one side to make a single run or to either side to make a double run. 

The arms can have a capacity of 20kg - 2000kg UDL.

Cantilever racking can be used to extend your storage into your yard by fitting a canopy to the top. Usually seen in timber merchants.