Probably something similar to these Felt Pads.
Great price....only about 4 bucks a piece!
About right for audio approved felt.
Has Ace now become an audio dealer?
Obviously a typo.....
Make sure they are marked "heavy duty".
If not, they tend to not hold up.
Also, if you move the speakers around a lot, you may find that the self-stick ones peel off.
If so, just glue them on with contact cement.
That's what I had to do.