We are fixing our storms. Some of the grey pile is disintegrating.... we tested out a scrap of new grey pile with a plastic fin down the middle from a friend.
its about 3/16" at base and 3/16" tall with the fin down the middle. It looks like your 58-021.
As long as your dimensions measure 3/16" by 3/16" like the 58-021, I agree that it should make a good replacement. Please let us know if you have any other questions. Thank you!