My favorite tension tools are ones I'nv made myself from the steel inserts in windsheild wipers. There are 2 primary styles of wipers, one has (2) flat thin steel pieces on either side of the rubber, and the other has (usually) one wider thin steel piece down the middle of the rubber. Look at the ends for two shiny spots for the first kind. *CAREFULLY* take them apart, and cut and bend those pieces of stainless into tension tools. The best method I've found for collecting these is to wait until a big rain storm, and go to the parking lot of an autoparts store. There will be a dozen or so old broken wiper blades in their garbage cans, but the steel inserts will be in great shape. They vary by thickness and width by brand and model, so you can get a large variety of subtly different tension tools. Use a flat jawed pliers and carefully bend them after cutting to length, and then sand the cut ends smooth, I go up to 400 or 800 grit wet dry paper depending on how worn out it is.