I think I want to replace the o-rings in the T-fittings between carbs - like the coolant, the air vent tubes, and the fuel tubes.

I have measured 4 different sizes: The carb coolant barbs use 1.5 mm (cross-section) x 5 mm (inside diameter), the fuel Ts (gray Ts) use 1.5 mm x 8 mm o-rings, the air vents (the brown Ts) use 2 mm x 8 mm o-rings, and the single black air vent T uses two 1.1 x 15 mm o-rings. I took all measurements from the actual o-rings as they came off my carbs using a micrometer.

I am buying nitrile Buna rubber, which is good for automotive fuels and coolant applications, durometer 70 o-rings. Honda of NA wants something like $40 or $50 for a few o-rings. I am buying all of these for under $8 from a manufacturer online.

Please tell me that the sizing that Honda uses isn't peculiar in some weird way that I haven't spotted!