"Actually, this is now so commonly confused as being a hat stretcher, that they are now reproduced and sold as ones. And yes they can be used as such, but they are not originally designed for this purpose. And this antique one wasn’t made for that. To add to the confusion, the real name is also similar. This is actually called a band stretcher. This device locks inside a brim block and holds the material tight inside the block while it is steamed. The size indication is a safety feature meant so you do not overstretch and break your brim block."