Mikuni VM22-133 - Main Jet Confusion

[Atipsyllama]

Hoping someone can shed some light on a main jet question I have. I ordered a Mikuni VM22-133, paid a little over $60 for it, and then ordered some new main and pilot jets. But as you can see in the picture below the main jets look different. The installed jet is round and has and O-ring and the main jet that I ordered (and was told to buy on multiple different sites) is hexagonal and has no O-ring.




There is no direct swap that I can find for this type of jet, the closest is a "press-on" jet and has no threads but looks the same with the o-ring. It looks like in the carb there is a place for the o-ring to seat against so I assume that needs to seal but I know nothing about carbs, maybe I am wrong.

Is my carb a fake and I got screwed? Does the main jet I bought work and the o-ring is not needed?

[Megadan]

I am going to go out on a limb here and say you got a reproduction mikuni.

That said, I don't see why the real main jet would not work in it. I see no reason why that jet needs an O ring. It isn't sealing against anything, so I will just assume it was some random goofy jet they installed because they had it on hand.

If it was me, I would just install the jet and rock it.