O-ring
An O-ring , also known as a packing or a toric joint , is a mechanical gasket in the shape of a torus; it is a loop of elastomer with a round cross-section , designed to be seated in a groove and compressed during assembly between two or more parts , creating a seal at the interface . 
<triplet> O-ring <subj> gasket <obj> subclass of <subj> torus <obj> shape <subj> seal <obj> use <triplet> gasket <subj> seal <obj> subclass of