I don't know what the proper name for it is but these were common on 50s CWC frames. They reduce the seat post size from 13/16" to the original standard 5/8" - you can use your old saddles without changing the clamp. As you can see I've de-rusted these completely so they function like brand new. Selling Price is $15.00 Shipped and $8.00 for each additional sent Priority Mail. If you are interested send me a message. Any questions just ask. Thank you for looking.