These are new old stock Mr. Gasket rear differential cover gaskets for the Chevy car 12 bolt rear ends. Will not fit the truck 12 bolts.

These are a high quality gasket made from the Ultra Seal III material so are very durable unlike cheaper paper gaskets. They are .037 thick. 

This listing is for a pair of them and they will be shipped between 2 sturdy pieces of cardboard as pictured in the last picture and not an envelope like other sellers.