Drill bit cuts a square hole

I don't speak Russian, but I do hear the universal language of expensive, specialized bits. This one, shown off by Mehamzog, drills square holes. This is a floating-head bit, I think? I guess if you actually set out to do this with things you can order post-world war II you'd end up using a broaching tool instead.

UPDATE: Veronica Connor writes: "This is called a rotary broach. He made a kinda home-brew version that is simpler in design than commercial ones (which is on brand for Russian machining channels) but that's what this is."