From the looks of it, that's a Schwinn badged AVA (a.k.a. Death Stem) and it already has a crack at the top of the expander wedge. Get rid of it ASAP.
You'll find stems compatible with the 21.1mm steerer tube under this search. Ignore the BMX type stems:
https://www.ebay.com/sch/i.html?_fro...+stem&_sacat=0
You may have to swap the bars too, though I dare say they are probably 1" bars shoved into the AVA.
-Kurt