Popular for use for a no weld oil pan oil return turbo inlet.

Fuel Cell / Tank Adapter Bulkhead Fitting
These high flow fuel cell / tank bulkhead fittings feature a reverse taper flare (radius) entry design.
This provides the maximum in unrestricted fuel flow without the turbulence of traditional bulkhead style fittings.
Fitting includes a locking nut and two poly-washers.