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A circlip (a portmanteau of circle and clip), also known as a C-Clip, Seeger ring, snap ring or Jesus clip, is a type of fastener or retaining ring consisting of a semi-flexible metal ring with open ends which can be snapped into place, into a machined groove on a dowel pin 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 bore or over a shaft. Circlips are often used to secure pinned connections.
When used to retain piston wrist pins (US) / gudgeon pins (UK), the clips are known as wrist pin clips or wrist pin retainers (US) or gudgeon pin clips (UK). The most commonly used circlip for this application is a simple spring steel circlip (snap ring US), or plain wire ring.
Common examples include e-clips (e-ring) and the (both internal and external) snap ring (US) or circlip (UK). These general types of fasteners are sized to provide an interference fit onto (or into, in the case of an internal fastener) a groove or land when in use, such that they must be elastically deformed in order to install or remove them.
The term "Jesus clip" comes from the propensity of the clips spring action when removing or installing. Typical remarks when the clip comes detached from the tool are "Oh Jesus, where did it go" or "Oh Jesus, we're gonna die."
Installation and lubrication
Since circlips are stamped out of sheet metal there is a smooth side and a rough side. To prevent potential damage, circlips are installed with the smooth side facing the part and the rough side facing out. Wet or dry lubrication is recommended to reduce friction against the circlip, maintaining its function.
Circlips are designed to be removed with special circlip pliers (snap ring tool US) which can be reassembled for internal or external clips, but in field expedient situations, a pair of needle-nose pliers (for internal clips) or leverage with a flat-headed screwdriver (internal or external) is sometimes used.
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