This is a proper airfoil shaped Velocity stack for a 50mm carburetor with a pod filter type flange (slip on). There is a version with or without a built-in screen, however, if printing with a screen, please use a Nylon-based material and not something that can break.
The velocity stack reduces intake drag because it smooths out the incoming airwaves and accelerates them increasing airflow and performance.
The airfoil shape on a full velocity stack acts as an airplane wing... in that, the high-speed air movement of air inside the horn creates an area of low pressure on the outside so it actually pulls air not just from the front part, but even from the under side of the horn (like a ducted fan).
To install, use a heat gun on low-medium heat to soften the material around the throat only enough to become slightly malleable and slip over the carburetor. It is designed to shrink over the carb as the plastic cools.
Print with the wide part of the horn flat against the table for both models. It was designed to print with no supports in this orientation.
This particular horn was calculated for a custom drag racing mini bike that uses a Predator 212 engine. With about 7.5" of intake before it, the stack creates a powerband right around 7000 RPM for a power boost.