Guiding rings (for the reciprocating motion)

In power hydraulics there are structural solutions for the piston and cylinder assembly in which guiding [full] rings are fitted in grooves [on the piston or in the cylinder] which also have the role of a sealing element. These rings are made of a PTFE composite material, e.g. T4WG, T4GM, T8B. The cross-section is a rectangle and it is obtained by machining [turning].