Thanks for the reply, Bob.
The "replacement" ones on the right are from a different brand carb, and I'm trying to find out the correct size I need. I'm thinking they might be a little bit small on the od.
They are probably 5mm od.
O Rings USA lists them in 1/2 mm size increments, ie 4.5, 5, 5.5, 6 etc. for $.04 each, so I ordered a bunch.