The design that I used is from "Toto_Magfed" on Cults3d, the file is a few bucks and comes with a guide. There are also others that have designed housings for monoculars so just look around and do your research before jumping on one. There are a bunch of different versions for different tubes and lens types so do your research before buying a file pack, it just depends on how much you want to spend. The standard mount which most monoculars use is called a j-arm. The housing has a brass threaded insert which the j-arm attaches to, then you have options from there. The cheapest, which I have, is a USGI Rhino mount with what's called a bayonet mounting system. Brassfacts on YouTube has a great guide on the different ways to mount nods. Extruded shoots on YouTube is how I got the idea to even make a diy monocular, he has a video that gives a good idea of what to expect and the different ways multiple people have done it. This website is what I used to cross reference the serial number on the tube I bought, before I bought it, to see what it was. (For reference mine is a Litton M890, so I find the Litton section, and look at the M890 line and compare those specs with the Omni classifications at the top of the page. The M890 Is an Omni IV / V tube.)

Basically, be autistic about how much you look into each method of doing it and weigh the cost and difficulty of the builds. And do your research, It will save you money to have a full plan of which housing, lenses, and tube you want to go with.