Dellorto 6413 6mm main jet 158 for round slide PHF and PHM carburetors as used on Guzzis and many other brand motorcycle applications including Ducati, Laverda, BMW.
Note these 6413 series jets are not used in square slide VHB carburetors used on Guzzis, the main jets for those carburators are 5mm 1486 series "pilot" jets.
VHB carburetors were standard on most US version big twin Guzzis from around 1970 until around 1980 including Ambassador, Eldorado, V7 Sport, 850T, T3, Convert, G5, SP1000, CX100. Many European version big twins used VHB carbs until the mid 80's, including V750 Special, 850 GT, California II, T4, T5, SP II.
Avoid costly and frustrating ordering errors, identify your carburetor before ordering jets.