All of the parts are available from any decent hardware store.
All of the main bolts, nuts and washers are 1/4" stainless.
The stainless steel HB transducer bracket is attached with 4 #8 stainless truss head screws and nylocks.
The metal is all 1/8" thick aluminum stock. The brackets were cut and shaped from a piece of 1" aluminum angle and the arms are cut from 1" aluminum flat stock.
I considered using the starboard corner mounting location but I would have to extend the Si transducer a minimum of 8"-10" to clear everything on the transom. There is just too much transducer dangling out there to do it that way. The other possible option on the starboard corner was to mount the Si transducer low enough that it had a clear shot under the hull but I did not want to expose it to the possibility of hitting something.
The best idea for my particular boat is the high mounted Si transducer coupled with the separate 2D transducer.