Dellorto 6413 6mm main jet 138 for round slide PHF, PHM and PHBH carburetors as used on Guzzis and many other brand motorcycle applications including Ducati, Laverda, BMW. 6413 series jets are used in a multitude of Dellorto carb types, thread size is 6mm x .75 pitch. A noteable Guzzi exception is the use of a 6413 6mm jet in the VHB carb used on the Nuovo Falcone.
Notes regarding 6413 series jets for VHB and PHBH carbs: These 6413 series jets are not used in the square slide VHB carburetors used on Guzzis, the main jets for those carburators are 5mm x .75 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, 850GT, California II, T4, T5, SP II. Also some US specification PHBH carburetors as used on V50 III, Monza, V65C, V65SP, V65TT and Lario models may use 5mm 1486 series jets as well, instead of the 6mm jets.
Avoid costly and frustrating ordering errors, identify your carburetor and/or jet diameter before ordering jets.