Product review (5 stars): Perfect replacement. Very fast shipping.
They wear out, you replace them, rinse and repeat. They're cheap and get the job done every time. I believe they are made to wear faster then the plastic teeth on the agitator, since that would be far more expensive to fix. I've replaced mine 3 times in 17 years since I had the machine and they've worked every time.

I keep buying only one set because I swear "next time I'll just get a new machine!!" Well here it is 17 years later and she's still going. So if your machine isn't very old I suggest buying a few sets and keep them safe for down the road.

EDIT: Forgot to add they said shipping might take up to 6 days but it was here in 2 so yeah, that's pretty cool too.