Never heard of them. Their company setup is pretty impressive. However to say 'relies on absolutely no one else for its supply chain' is an extreme exaggeration and frankly impossible.
They don't make the computers, fiber optics, switches, exchanges, or software that their web site requires to run. They don't own the fleet of trucks, boats, and planes required to get their product to their customers - or their raw materials from plant to plant. They likely use rubber mats in their plants but I don't think they have a rubber plant. Unless they use outhouses I'm pretty sure they don't make toilets and sinks and plumbing. I don't know if they produce their own electricity but I'm sure they didn't build a generating plant from scratch....and on and on it can go.
If you haven't read it, search for the essay - I, Pencil - I'm sure YKK uses pencils as well.
The point is noone is even remotely close to being their own supply chain every one is deeply dependent.