Suzuki published the actual size in some of their parts diagrams but it's very odd .....
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I've used the 1mm x 4mm size for many years but may try the slightly smaller 1mm x 3.5mm at some point. I've never even seen a 1.1mm diameter o-ring listed for sale anywhere. You can actually still buy the Suzuki one, if you don't mind paying that much for one o-ring.