These seats used to be a standard item. However I don't see them listed any more. Defender has item number: 650443 folding helmsman seat, but no back rest and only 10" diameter. Boaters world has Garelick # 16-648-1093 Neither of these have the back. I had one on an Owen's Sea Skiff I owned in 1961, which had two brackets on the side of the coming, which had 3/8" ss pipe, and then ss pipe welded to the bottom plywood board of the seat, and a rod going through the pipes. There was a single leg, which locked down (any RV store will have the catch for these), with a crutch tip on it. The back was also plywood, padded, and had brackets similar to the bass boat seats. This is basically a SS L bracket--about 3" on the bottom, 4" high, rounded at the top, and attatched to another SS bracket on the back, the bottom of the back, hits the bottom of the seat and cannot go further back. You can have the SS parts made at any fabricator (could be alumium and DIY) and use foam and upholustry. Interesting that an item which was on almost every boat 45 years ago, is not easy to find today! Regard, Bob Austin