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

The term for the unobstructed open edge of a fixture is referred to as the rim. In the context of sanitation and plumbing fixtures, the rim is a critical design feature that ensures proper flow and drainage of water. It allows water to flow freely without any obstructions, preventing issues like overflow or improper drainage.

Understanding the function of the rim is essential in various applications, such as sinks, toilets, and bathtubs, where it plays a vital role in the overall functionality of the fixture. The rim's design can also affect hygiene, as it helps in directing the flow of water effectively to wash away waste and maintain cleanliness.

The other terms listed, while related to plumbing and fixtures, do not specifically define the unobstructed open edge. Flushing surface relates to areas designed to enhance cleaning performance, a blister is not commonly associated with fixtures, and a drain board is a surface used for draining dishes and does not pertain to the edge of fixtures directly. Thus, the correct identification of the rim highlights an important aspect of fixture design and sanitation.