The venturi hole is Ø 26mm and perfectly fits carburetors of this size. To adapt it to smaller carburetors, it is necessary to file the first part of the carburetor's intake duct. To adapt it to carburetors with a diameter greater than 26mm, it is necessary to slightly file the venturi to fit the carburetor's diameter.
Advantages:

Improves engine performance
Increases power, acceleration, and top speed
Compatibility with carburetors with or without a mixer
Possibility to mount an air filter directly in the box
Stylish and classic look
Non-deformable aluminum body