Circlips, sometimes known as retaining rings or snap rings, are fasteners used in various applications. They are an opened ended semi-flexible metal ring that are snapped or clipped into a machined groove. There main function is to prevent lateral movement, whilst not impeding on the rotary motion of the shaft.
Even though there are various styles of circlip or retaining ring. They mainly fit in two ways. Internally or externally. Internal circlips are fitted into a bore and are sized relative to the bore into which they are to fit. External circlips are fitted over a shaft and are sized relative to the recommended shaft size to which they are to be fitted.