I successfully used one to resize an old Pilgrim I bought off of Ebay. I am more of a long oval and the hat was VERY round. I just put the stretcher in it, stretched it and steamed it and let it cool and now it fits nicely. Just be careful how much pressure you put on the sweat so you don't break any stitches. Be particularly careful with vintage hats. I don't see why there would be a problem using it with mild pressure to maintain the size of a hat either.