I believe its that little black plastic thingie, thats glued somewhere inconspicuous on a package. I find them on CD's and DVD's primarily.
GREAT idea!!! I just had a friend resupply my stock, he works at a machine shop and gets me a piece of every size and material in stock!! LUCKY me!! Brass, flame hardened (BLUE STEEL) and mild steel. It coms in might handy!!
CW