This is a aftermarket non standard main jet to fit quite a few Yamaha / Mikuni carbs  RD 50, 80, 125, 200, 250, 350, 400, 500 LC

DT 50, 80, 100, 125, 200, 250,

RS100, 125, 200.  RXS100

For Mikuni carbs only

Made in Japan

This is not the standard size, It can be used to upjet or downjet your carb when needed.

I have other sizes listed 

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