This is great as a razor blade smash routine as shown but, do you have Lockey? These envelopes can
be usedfor this as well.
Each key is put in an envelope. If you want to number them and do a
prediction, fine. But you can also have the spectator choose a lock to lock the box.
Pick the
envelopes up and, one by one, discard them through the Lockey box slot (they fit!). You find the
envelope with the key that works.
This is definitely a utility prop.