When students try to twist off the mouth pieces for the spirometer (instead of puling them straight out), the mouth piece posts can be broken off into the handle. To remove these stubs, use a T-8 driver to loosen the screws from the bottom of the spirometer handle.
This will allow you to separate the two halves of the spriometer handle and will expose more of the stubs. These can be gently removed by gently pushing the stubs straight out with a pencil or pen.
When the stubs have been cleared, reattach the lower part of the spriometer such that the recess on the top of the spriometer is on the same side as the clear tubing that extends from the bottom of the spriometer handle.