Made for Lux-Tool 150mm.
https://www.obi.at/pruefwerkzeuge-messwerkzeuge/lux-schieblehre-comfort-150-mm/p/1153709
Because the case they sell with it is sh*t, bulky and fragile if you transport it.
Here you just clip it on. It can be tight - but it holds inside unless you get it out.
The author marked this model as their own original creation.