What is the use of circlip and Oring in machines?

A Circlip can be defined as a retaining ring which can be used internally or externally, primarily used in a bore to secure pinned connections , which will allow rotation but prevent any lateral movement .

A Circlip can be defined as a retaining ring which can be used internally or externally, primarily used in a bore to secure pinned connections , which will allow rotation but prevent any lateral movement .

An O-Ring can  be  defined as a mechanical gasket made usually of an elastomer material, which sits in a groove  or recess and compressed  between, primarily two static faces to prevent fluid leakage, Where three is rotation between one of the two sealing faces  such as shafts , then Lip seals are the preferred choice.   

A circlip is used to hold or limit axial (typically) motion an assembly in place. It acts as a stop within a tolerance band.

An o-ring is specifically used to prevent fluid leaks. It is a sealing device.