A circlip is also known as snap ring. It is a type of fastener consisting of a semi-flexible metal ring with open ends which can be snapped into place, into a machined groove on a cylinder plug or other part to permit rotation but to prevent lateral movement. There are two basic types: internal and external, referring to whether they are fitted into a tube or over a shaft. Circlips are often used to secure pinned connections. Circlips are fitted may be removed with a pair of needle-nosed pliers or a special snap ring tool.