Sorry for my ignorance but why is the .500-28 adapter needed? My other threaded barrels fit nicely into the suppressor. Thank you. — 3 Answers

The simple answer is the barrel's outside diameter is smaller than 1/2". Therefore to be able to thread on a suppressor that requires 1/2x28, a larger diameter adaptor must be threaded on the smaller diameter barrel. Also, Glock can't just machine the end of the barrel with larger 1/2x28 threaded end or you would not be able to remove the barrel from the slide.

OEM barrel not big enough to accommodate a 1/2x28 thread. That’s the real reason for the adapter. If you own almost any type of Glock, this is a great practice handgun. Use 40 grain round nose .22 for awhile. Say 500-1000 rounds. After that, everything should be worked in well and the gun will eat anything. I like having an extra 1/2” of barrel, even without a suppressor. More barrel= better accuracy, and distance. CCI Velocitor @1435 FPS makes this a pretty good carry option if you a want light gun. Put on G19 night sights (I used Fision) and a laser underneath (cm-206 is what I used) and you’ve got a full package. Use a Fobus holster and modify holster end to fit. Takes some work to get it all worked out. But quite an accurate weapon when completed. Use high quality ammo if you carry a .22. CCI Velocitor. Always goes bang, and circulates the weapon back into battery.