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Ring-shaped packing materials used to pack oil and gas drilling equipment, comprised of milled steel

Ring-shaped packing materials used to pack oil and gas pumping equipment, comprised of one or more of the following, fabricated thermoplastic compounds, carbon-filled polytetrafluoroethylene (PTFE), nitrile rubber (NBR), hydrogenated nitrile rubber (HNBR), polyurethane (PU), ultra-high molecular polyethylene (UHMWPE)