My oboe instructor makes/tunes my oboe reeds. Every time he scrapes the reeds, he inserts a piece of plastic(?) into the reeds. What's that piece of plastic called? It's a bit wider than the reeds, round on one end and a bit slimmer on the other end.
The plaque lets your teacher scrape the tip of the reed w/out damaging the tip (though students can still take chunks out of the tip with dull knives, as can pros). It's a very useful tool. It also helps you to see if the tip is thick enough. There are too many uses for a plaque.