Most Digitran switch series are composed of a number of "building blocks" which can be selected by, the user and grouped together into any combination to provide a unitised digital switch assembly tailored exactly to suit the application. These building blocks or "modules" consist of: Switch modules of various types, including double modules capable of performing a vast number of different switching functions. Module spacers to separate switch modules that perform different functions, or to identify different digital parameters, or define input information. Message units: extra-wide switch modules to provide additional space for characters or legends. End brackets: (one for each end of an assembly) used to complete the assembly and provide a means of mounting the unit. Threaded rods or "assembly straps" to hold the assembly together. Mounting hardware such as screws, nuts and washers for use in mounting the assembly to the equipment control panel are also supplied.