Double rods: You will need to purchase two size rods that are the same in finish: a larger one for the front rod and a smaller one for the back sheer rod. Install the larger rod first and then just on the inside of that bracket, install the smaller rod’s bracket.
My double industrial conduit curtain rod. I made this with pipe fitting and electrical conduit. Pipe fittings cost $15.00, conduit and spray paint cost $13.00. Cost per window is about $28.00 in Oregon where we have no sales tax.