As mentioned the "standard" at least up through 19-4 was the .265 grooved "service" trigger. They could also be had with a .312 smooth Combat" trigger.

If ordering one you could order it with anything that would fit.

Most LEOs I worked with replaced the thin grooved trigger with either the .312 or .400 smooth "combat" trigger, which is much more comfortable in DA use.

A quick look shows all of my 4" 19s have the .400 smooth trigger and the 2 1/2" 19s have the smooth .312 trigger. I'm sure were ordered that way and others modified after they were purchased.

The 6" ones have the grooved .400 "target" triggers and the .500 hammer. Again either ordered that way or modified after purchase.
A 19-2 6" gun I got from a Forum member had the narrow grooved trigger but I have since replaced it to match the others.

RWT