This intake manifold is most commonly (but most exclusively) used for GY6 50cc Engines. This engine is most commonly used for 50cc gas scooters, as well as smaller dirt bikes, ATVs and buggies / go karts.
Manifold Inner Diameter: 18.4mm
Mounting Holes (center to center): 45.0mm
Breather Inner Diameter: 25.8mm
Breather Outer Diameter: 37.0mm