Just picked up a new one, as in unfired I won on GB. Noticed the plastic guide rod, ordered a steel one for it. Barrel is threaded, supposedly 1/2 by 28. Tried a suppressor I had for my Glock 17 and it won't thread on. What I'm I not seeing ? Is the Beretta barrel a different thread pitch ?

I have a G17 with a factory threaded barrel. It's metric and reverse thread.

Don't remember off the top of my head and not home right now.

I believe the 92A1 threaded barrel uses a Metric 14X1RH thread pitch and not 1/2X28.

Beretta 92a1 was available in both 14x1 RH and 1/2x28 (suppressor ready model).  They have different SCU numbers so it’s easy to check.  1/2x28 had an o-ring on the barrel and not inside the thread protector.  Also, if you can remove the barrel from the slide with the thread protector still on that should be the 1/2x28 version.

I have run into a pistons from one manufacturer that were poorly threaded and would go on Glock 1/2x28 barrels but  not on Beretta and barely on a 1911.  A brand swap fixed that.

I put the barrels up against each other the 14x1 is thicker than the 1/2x28 so I could have sent it off to a reputable machinist and had it rethreaded. I opted to just order another barrel in 1/2 x 28.