Specifies the properties of the various lead units used in the construction of shielded enclosures: basic units (bricks, posts) and functional units (aperture bricks, windows, sphere units, plugs and reducing units). Only one and two chevron bricks are standardized. The units are classified into 3 categories: standardized units; units which are either used very infrequently or for very specialized purposes, or are used very frequently in one country and it is felt that this use will become more widespread; units which are acceptable for a transition period.