Centering Ring KF 25 With Viton® O-Ring, KF 25 (NW 25), Stainless Steel, The centering ring contains a rubber elastomeric o-ring. Those are also recognized as NW10, NW16, NW25, NW40, or KF-10
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https://www.allworldmachinery.com/itemdetail/P-25
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R-25 O-Ring (ID: 33 mm, CS: 3.5 mm, OD: 40 mm) by X1 Tools (10 to 120 O- Rings) | eBay