I thought I posted this way-back-when under one of my "Random Tips" rambles I get on now and then but cannot find it. This was just going to be a "hey I made some more of these" thread but just in case I really didn't post them before, here goes . . .
You dig through the scrap bin and find a small panel and some scrap that can be cut into a triangle profile as shown.
Glue the triangle strip on one edge or on both edges if your panel is large enough. I end up with an item that is about 7" long when completely done.
Slice it into 1-1/4" wide strips on the table saw.
Cut those strips in half and add a hole to hang or string them on when not in use.
Cut some abrasive strips. I use 400 grit but anything down to about 220 is fine. Once you get coarser than that you risk damaging the frame part surfaces.
Stick the abrasive strips onto the thing-a-ma-bobs.
And you use them like so.
I had a batch of these but cannot find them post-move (yet) and so whipped up another batch this morning.