An internal imperial circlip (also known as an internal retaining ring) is a semi-flexible metal retaining fastener designed to be installed inside a bore, housing, or pipe. They fit securely into a machined groove, creating a shoulder that holds components (such as bearings, gears, or pins) securely in place. The term “imperial” means its dimensions, tolerances, and the grooves it fits into are measured in inches, conforming to British (BS) or American (ANSI/ASME) standards.