PTFE covered rings

This type of joint is composed of a core of fluorocarbon elastomer (FKM) or silicone (VMQ) wrapped in a sealed FEP or PFA.
O-rings are sheathed elements with double sealing effect, the sealing sheath, so that the O-ring as an elastic element is pre-clamping.
They are mainly used in static application (axial or radial).