So I've really already learned this by experience with my oscillating belt sander that you don't buy excess belts and keep them laying around for a long time as the adhesive joint will age and deteriorate. Then when you do need "that" belt, it WILL fail!...guaranteed! So yesterday I needed to use my belt sander to level a bunch of uneven glue joints on some larger panels. I had about 10 new belts that are ...I don't know how many years old! Yup, every single one of then had the adhesive joint fail within 30 seconds or less of spinning them up on the belt sander! So don't ever keep more than you're going to use! It's a waste of time and money!