boss

Standards

a connection on a vessel, pipe or fitting, provided to facilitate the connection of a pipe or fitting

Source - AS/NZS 3500.0:2003: Plumbing and drainage

HB50

<covering> ornamental knob or projection covering the intersection of ribs in a vault or ceiling, often carved with foliage

Found also at the intersection of wooden beams, or placed at the end of a cantilever.

<pipe fitting> connection on a vessel, pipe or fitting, provided to facilitate the connection of a pipe or fitting