Product review (1 stars): dont buy this version buy the all plastic one
The inside metal ring is supposed to make these 'heavy duty' but it does not. It actually makes it less heavy duty.  I just replaced mine and it was of this type.  I bought this heavy duty type thinking it would last longer but it does not.  If you think about it, the metal ring in essence makes the motor drive shaft large and makes the plastic connecting the three arms smaller.  this makes those connections even more prone to breakage. That's exactly what happened to my version like this. It broke between those skinny plastic connections between the arms.  This happened less than a year after installment  I replaced it with the all plastic version which lasts years.