Earl S. Tupper began experimenting with plastics in 1938 and by 1945 had produced his first tumbler. Tupperware Home Parties was formed in 1951 to sell products through dealers using a party plan. Here are five clean Tupperware tumbler seals. They measure 2 3/4” in diameter from the underside outer rims. They are marked “Tupperware ‘F’ Made in USA". They fit the 12 ounce tumbler.