An O-ring is a seal made from round cord or as a molded part. Selection requires the inside diameter, cord section and groove dimensions.
Inside diameter follows the groove or the shaft the ring stretches onto. Section is the cord diameter, often 1.5–8 mm on valves and pumps. Do not swap them: a 20×3 ring and a 3×20 ring are different parts.
A static joint and a moving assembly need different compression. On a rod or piston, account for clearance, pressure and direction of movement; on a cover, uniform seating without twisting is more important.
NBR is recommended for oil and hydraulics up to +120 °C. EPDM for water, steam and outdoors. FKM for hot oil and fuel. Under pressure the section has to match the groove: too thick will not enter, too thin will not seal.
On a flattened sample we measure the cord away from the crushed spot, and the seat if the photo shows it. A badly stretched sample overstates the inside diameter.
We make the batch in Tashkent, not “the nearest size from stock”. After approval, usually 3–5 business days. +998 90 944 99 40.
