Don't the cavemen have the patent on wheels? hahah Seems like you could put wheels on anything you wanted and not have legal problems over it. Danmar's real problem is with China. Either Danmar didn't pay for the exclusivity of those parts or they did and China doesn't care and sells them to other people too.
It just comes down to legal bs. Danmar is probably only working with one factory in China for their product. They may have an exclusive deal with them, but other factories don't have to follow that a deal. Getting the patent issued and then enforced in China is basically impossible, especially for a small foreign company.
So Danmar did the next logical thing to have some "exclusive," rights. They got a US patent for being portable. I haven't looked up their patents or any of this case, but I'm betting their is a patent exactly talking about portable towers that wheel around and bolt into floor anchors.
Since basically every lift on the market uses towers and bolt to the ground, that was likely not deemed patentable. But they were the first to put wheels on it, so they had a unique idea that they were able to get through the patent office.
It's always joked that you can take an idea that is in the public domain, put a clock on it and get a patent. (basically taking two free designs and putting them together to make a "new one) Danmar basically did that, only instead of a clock, they used wheels. But that means the only unique and patentable part of their idea is the wheels. So NAT can build the whole damn thing, and forget to include the wheels, and be good.
). Based on your info and what I've read this seems like fairly robust design for a home hobbyist garage lift. I only mention the Mohawk design because I may have the opportunity to get a a used A-7 for about the same price. I'll have to wait and see what's being offered. Thanks again for the info.