I agree with Ken, it's a commercial product. I have a box full of them. You generally see them on Phelps and earlier Star's like the one in the eBay listing. They don't seem to fit as well on later model Stars. There is a Clockwork type spring under the big pulley and it's very susceptible to breakage. Replacements are hard to come by.
The machine in the eBay listing is a Star Progressive, but has several of Phelps parts.
Bruce Williams