A half moon ring spanner, also known as a half-moon wrench or offset ring spanner, is a specialized hand tool designed for accessing and turning fasteners in tight or hard-to-reach spaces. It gets its name from its unique shape, resembling a half moon or crescent.

The half moon ring spanner features a curved or angled ring-shaped end on one or both sides, allowing it to reach fasteners that a straight spanner or socket wrench cannot access directly. The curved design provides additional clearance and allows the spanner to be used at an angle, accommodating obstacles such as pipes, protruding parts, or other obstructions.

This type of spanner is commonly used in automotive, plumbing, and machinery applications, particularly when working on engines, piping systems, or machinery components located in cramped spaces. The half moon ring spanner's design enables technicians and mechanics to tighten or loosen fasteners effectively in confined areas where a regular spanner may not fit or operate comfortably.