In Building services engineering and HVAC, a bell mouth is a tapered expanding or reducing opening in the end of a ventilation duct, so named because the taper can resemble that of a bell shape. They are primarily designed and used for return air or extract air purposes within building ventilation systems, more commonly located within ceiling void...
Bell-shaped air intake fitted to some carburettors.
The flaring or tapering of a machined hole, usually made at the entrance end because of misalignment or spring of the cutting tool.
The flaring or tapering of a machined hole, usually made at the entrance end because of misalignment or spring of the cutting tool. 
Bell-shaped air intake fitted to some carburetors.