Rectangular cross section. For static and dynamic use. Reciprocating and rotating movements possible. Material: PTFE. Back-up Rings are installed together with Trelleborg O-Rings and Quad-Ring® Seals to prevent extrusion in applications above 5 MPa / 725 psi. Available in spiral, cut, or uncut designs in unfilled PTFE, based on ISO 3601, AS 568.