This is a Stainless Steel 9mm Conversion Barrel for a Glock 22 Gen 1-4

This will turn your Glock 22 (.40 cal) into a Glock 17 (9mm).

Just remove the .40 cal Glock 22 Barrel from your slide and "drop in" this 9mm Conversion Barrel, and you have the ability to shoot 9mm ammunition out of your Glock 22.