I'm not a metric person but pipe threads are designed to the same standards whether it be metal or PVC. So any 19mm thread should fit any other. Now here is a twist to that. You have tapered pipe thread and you have straight pipe thread. They don't work well together.
As far as PVC goes, they make it as schedule 40, 80 and 160 which means wall thickness changes but the outer diameter remains the same. I always use schedule 40 for my plumbing and 80 for floating features in my ponds like feeding rings.