Modulex Modulex was a building system that was designed for adults . It was developed by The LEGO Group at the same time as their Modulex sets were produced from 1963 until 1965 , and were exclusively available in parts packs by colour . The LEGO Group made Modulex a separate company in 1965 , and the text " " LEGO " " was removed from the studs and replaced with " " M " " . Description . Modulex bricks were formed with a cube type 5 to 5 width / length ratio , meaning that , unlike very nearly every product produced by The LEGO Group , they were not compatible with LEGO bricks , which have a 6 . 5 to 5 width / length ratio . Modulex bricks were available in a wide array of unusual colours , shapes , and sizes . The idea for the Modulex brick came at an unknown time in the early 1960 ' s , when Godtfred Kirk Christiansen was attempting to create a model for the house he was building out of LEGO bricks . To his surprise , he found he was unable to do it accurately , as LEGO bricks had an aspect ration of 6 : 5 , rather than the European standard of 1 : 1 . Rather than build his model out of scale , Godtfred had a uniquely sized line of parts moulded for him , that would allow him to copy his plans more exactly . History . After some thought , Godtfred realised that LEGO bricks in this size developed specifically for architectural planning and modelling might actually be a successful and commercially viable product , and so Modulex was born . Through an unusual coincidence , at the same time when Modulex was being designed , the Architecture System of sets such as 750 Hobby and Model Box , 751 Hobby and Model Box , and 752 Hobby and Model Box were released . Despite the similarity of premise and release date , there is no definitive proof of a connection between Modulex and Architecture . First off , LEGO created a subsidiary company , Modulex A / S ( although the name is reported to vary ) , specifically to sell Modulex products , the first of which , the " M20 System " , was released in 1963 . The system consisted of a series of bricks including everything from windows to simple 2X4s and slopes , in addition to several more unusual items , such as unique baseplate foil , foil combs and cutters , and , uniquely for LEGO , solvent - based glue to stick models together after construction . The line was intended for building in 1 : 20 scale ( hence the name M20 ) . M20 sets were available mainly in sets containing an assortment of bricks , but they were also available in bulk . M20 didn ' t do very well with architects , who were , after all , the target audience , but it had became quite popular with industrial planners . So , in 1966 , Modulex split into a separate company from LEGO ( although they were still owned by the group ) , and released the Modulex Planning System , specifically designed for use by this demographic . The Modulex Planning System , featuring bricks rebranded with an " M " logo on the studs , included plates , tiles , and blocks with letters printed on them . After several further years of producing bricks , Modulex underwent a major change with the release of " Interior 10 " , an architectural signage system . Although based on some of the ideas of the Planning System , " Interior 10 " and the 1979 - introduced " Exterior 500 " finally brought the company away from the ideas of LEGO entirely . In 1993 , Modulex merged with ASI Sign Systems , and is currently the most successful signage company in the world , with subsidiaries in more than thirty - five countries . However , the LEGO - style planning system was not entirely forgotten , with " Plancopy " , introduced in 1982 , and updated in 1994 . " Plancopy " is still available to this day .