Duct grill with both a male and female end.
A remix of my female-only "end cap" grate.
As with any custom fabricated object, use materials appropriate for the application. If any kind of heat or fire resistance is needed, use a metal part. ABS filament with fire-retardant additives may also be a viable option.
The author remixed this model.
Converted from a female end cap to male+female inline.