Product review (4 stars): Excellent, but make sure the damper is working...
Broan Roof Cap 634m

I installed two of these low profile roof caps on the roof of a new addition.  See Customer Images.  Exhaust fans from the home's interior connect to the 6" round duct on the cap's bottom.  These roof caps are well made, look great on the finished roof, and work well in being the exit point for exhaust fans.  A bird-screen wire mesh is installed, which you can just barely see in one of the Customer Images.

They are painted a very dark brown, not "black" as stated in the Amazon ad.  On the other hand, you can only tell they are brown from close-up - at any distance at all they look black.

After installing, check from the inside that the gravity-operated aluminum damper is working properly.  A damper on one of those roof caps came loose during installation.  The damper pivots on two tiny tips, either one of which can pop out of its pivot "hole" during delivery or installation.  You need great patience (small hands help) to get it back in place; I did it from the inside after it was installed.

One star off for a design that allows a damper to pop loose so easily.

Recommended.