Plain concept is revolutionary, used regularly as template (7)
I believe the answer is:
stencil
'template' is the definition.
(I've seen this before)
I cannot understand how the rest of the clue works.
(Other definitions for stencil that I've seen before include "Clients for copying device" , "Method of decorating" , "Text template" , "It's perforated for ink or paint to pass through" , "Cut-out for painting patterns or shapes" .)