Chipboard O-Card flats for audio cassettes. By adding 1 item to your cart you are buying 100 O-Cards. To buy 500 O-Cards add 5 items to your cart. Make your own audio cassette O-Cards! The board is uncoated so you can use a variety of printing methods - stamps, silkscreen, inkjet. Prescored for easy folding and gluing. Made with 16 point brown chipboard. 100% PCW.