I have been searching online for a source of brass threaded inserts to convert them into urn threads. Sadly, my friend Rick Brantley passed away. I do not think his son will be picking up the business. My favorite size is 3.5 in. I do not even know what I'm looking for. Brass threaded plumbing couplers? Rick told me it wasn't that hard to do it. He did it on his lathe, with turning tools. Found some on a plumbing site, but a 4 in threaded brass something, I think for a bathtub is $97. I'm planning on wandering through the aisles of Lowe's and Home Depot. Any insight will be greatly appreciated.