Flexi box Flexi-box transmission line kit The flexi-box is a screened, rf or microwave, project box that is milled from an aluminium casting and then alochromed. It can be fitted with up to four sma, bnc or n type connectors, male or female and in any combination. The sma and n type connectors supplied, have a non-standard (11/16") flange and are specially manufactured for use with this box. [parts used to make the transmission line kit] component parts of the flexi-box kit. These small rf test aids are built in the flexi-box, which is a small aluminium screened rf enclosure. They can be assembled by you or supplied ready built and tested