Throat Check Tool
The Throat Check Tool lets you check the throat size of your mouthpiece.
There are three sizes:
#28 - #19 -- contains all sizes from #28 to #19, this will work for most trumpet mouthpieces.
#29 - #15 -- contains all sizes from #29 to #15, this will work for those trumpet, cornet, and flugelhorn mouthpieces that have throats up to a #15.
#30 - #1 -- contains all sizes from #30 to #1, this will work for just about any trumpet, cornet, flugelhorn, french horn, and some trombone mouthpieces.