The umm number 7 faucet O rings, you can get a bag full for cheap at Lowes or Home Depot.
Thanks... when I search online (I'm in Canada) for my local HomeDepot, Lowes, etc o-ring stock nothing comes up with that description... they have actualy sizes for the most part such as "2 Pack 11/16" ID x 7/8" OD Faucet O-Rings" or whatever... is "umm" an actual thing or you just typing "ummmmmm" lol? I do see O-rings described as for a faucet, but nothing that mentions umm number 7.... Maybe it's an American thing?
Dave
UPDATE: haha no sooner did I post this I tried googling "number 7 o-ring" and found a 10 pack on HomeDepot.com... I'll poke around homedepot.ca again.. I do see the equivalent measurements now tho, from that item on the .com page, "3/8 in. I.D. x 1/2 in. O.D. x 1/16 in. wall thickness"