These are chair leg slides that can be purchased at any hardware department. They come in several different sizes.

A 1/4" hole is punched through the center to fit on the bobbin shaft screw. I large area washer is used on each side to compress the slide against the spool when the wing nut is tightened. In this case I used a nut recessed in a draw knob.

I did not come up with this idea, got it from a local friend. It works better than any spring tension I have used. In using this tension device for wrapping rods, there is no drag on the thread itself. The thread comes off the spool direct to the rod.