I've noticed some of the fittings for pvc water pipes have brass threads. I'm wondering if they are supposed to be better than plastic threads, or are they for a special purpose?

I am pretty sure brass fittings are stronger.

If the pipes have no pressure than probably plastic is good enough.

1 hour ago, OneMoreFarang said:

If the pipes have no pressure than probably plastic is good enough.

Plastic has worked fine for pressurized pipe for decades before brass was available.  It continues to work fine in most installations.  I have a bunch of 20+year old plastic threaded fittings that probably will be good for another 20 years.

3 hours ago, zlodnick said:

I've noticed some of the fittings for pvc water pipes have brass threads. I'm wondering if they are supposed to be better than plastic threads, or are they for a special purpose?

They are better when you are fitting a metal attachment (tap etc) to the pipe. But be careful that you do not over-tighten the fitting or the plastic surrounding the brass will break.

In theory better, however I have had 2 separate cases where the in-mold brass thread has cracked leading to leak.

 

Probably would not have had problem with plastic-only one. I will not use brass ones any more due to bad experiences