doepfer amongst others make them - available at most modular stores worldwide... for only a few $/€/£...

although 1hp gaps aren't that bad (screws can get in but patch cables probably can't) and can be helpful with regards to cooling...

"some of the best base-level info to remember can be found in Jim's sigfile" @Lugia

Utility modules are the dull polish that makes the shiny modules actually shine!!!

sound sources < sound modifiers < modulation sources < utilities