Modulex was a building system that was designed for adults. It was developed by The LEGO Group at the same time as their Architecture System of sets 750 Hobby and Model Box 751 Hobby and Model Box, and 752 Hobby and Model Box. Several sets were produced from 1963 until 1965. The LEGO Group made Modulex a separate company in 1965, and the text "LEGO" was removed from the studs and replaced with "M". Modulex was and is not compatible with LEGO elements.