The widespread popularity of the industrial plug-in type of mounting used the 219 frame relays results in many requests for the plug-in enclosure only. Some requests originate from a desire to match relays on the same panel, but many stem from applications requiring no relays. These modules are furnished as disassembled kits of parts which include all necessary hardware. Many design engineers find these plug-in assemblies ideal for conveniently and quickly modularizing their control circuitry. Combinations of relays, resistors, capacitors, transforms, rectifiers and innumerable solid state devices are often combined in these envelopes to form pre-wired, pre-tested, sub-assemblies, or complete controls on some machines..
