I happened onto an antique screw plate buried in my collection and decided to finally mention it. It looks like this except that the tightening screw is a matching handle with a cross hole for a tommy bar. It shows how to form screw threads starting with only blacksmith tools.
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The blocks separate to accept an unthreaded rod. The thread grooves are nearly straight and look to me like they could have been cut with a vee shaped chisel. I suspect the slight rounding they show was from wear. It swages threads into the rod instead of cutting them, which I've read is better for wrought iron which has a grain of iron and slag residue from forging that might fall apart if it's cut. https://thecarpentryway.blog/2012/12/wrought-havoc/ It can create a matching tap by threading an annealed carbon steel rod which then has cutting grooves filed in the end and is hardened. Cutting tool grooves were hand filed until Brown and Sharpe introduced a universal milling machine to cut them during the Civil War.
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When I visited the museum many years ago it was in the attic along with many other important inventions awaiting restoration. I was photographing their antiques with one of mine, a 1936 Leica that charmed the curator into showing me the old Leica he owned, and allowing me upstairs.