What is the term for the unobstructed open edge of a fixture?

The correct term for the unobstructed open edge of a fixture is "rim." In plumbing terminology, the rim is a critical feature of fixtures such as sinks, bathtubs, and toilets. It is specifically designed to provide a boundary for the water to contain within the fixture, as well as to support certain functions, such as holding water or allowing for overflow protection. The design and structure of the rim ensure that it effectively channels water while preventing spillage and enabling proper drainage.

Understanding the precise vocabulary in plumbing is important for effective communication and for compliance with code standards. The term "rim" specifically denotes this circumferential feature, distinguishing it from other related terms that may have broader or different meanings, such as "edge," "boundary," or "top." These terms do not specifically convey the same structural or functional attributes associated with the term "rim" in the context of plumbing fixtures.