My DIY Differential Spreader for my Spitfire, I designed it in my Rhino CAD. Built from steel plate, steel bar, brass, nylon, grade8 all thread, grade 8 bolts, washers, nylocs and paint. I have a machinist friend who has a mill and lathe (large) in his basement, I had him machine the 12 sided nut and threads for the adjusting mechanism, I used his mill while he was turning that stuff on the lathe, to mill out the holes and slots for the arms. He had another friend of his that had a CNC plasma cutter in his garage, so I took my CAD files for the plates and converted them to DXF files and we cut them out on his table.