I don't know how you store your spools....but I'm thinking......I've seen some of those little beads with holes in them (usually you see them with letters--but I was able to find some with numbers). Anyway....maybe string the number of the thread on a little rubber band. Then, when you take it off your machine...put the rubber band around the thread spool? Or maybe you can come up with a little dowel with the number written on it (or the numbers glued on it) and then stick the dowel in the spool hole. Or, last but not least, there are these little baggies that I use for DMC embroidery thread....there's a place to write the number on the sack (those are skeins, but might work for your spools?). Have fun!