Product review (5 stars): This fit perfectly on my Whirlpool agitator....
This fit perfectly on my Whirlpool agitator.  I ordered on Thursday.  It shipped Friday.  On Monday, it arrived.  I opened the box.  Set it in place.  Slid down the ring to tighten.  Done!
This was painless and it sure beats trying to time the rinse cycle.  Great product for the do it yourself market!!