I use the thread on wooden spools...have tons of them. Unwind the outer layer, see if you can break the thread by pulling it, and if it doesn't break it's as good as any new thread to use. Most of mine are from the 60's and 70's when I was into sewing full swing, but some (my mother's) date back to the 40's. All of it remains strong and I see no reason not to use it.