Product review (4 stars): Purchase two - after making cleaning the old ones
I purchased these as a part of a larger dryer overhaul.  Turns out I didn't need them, but may someday.
Your dryer will need two, but they are sold individually.

Contrary to what is on the internet, these can be replaced in my dryer in about 10 minutes - before I did so, I cleaned the old ones with steel wool and alcohol and they work great.  Problem is apparently a film left by dryer sheets.