The ID19 OD24 CS2.5 O ring, NBR nitrile rubber, 19 inner diameter, 24 outer diameter, 2.5 cord, a standard size, the figures consistent, the inner plus twice the cord equals the outer. It sits in the groove, the two halves come together, the ring is squeezed flat, and the gap is filled, no oil, water or gas weeps. It resists oil, fuel and heat and holds its spring, and black means NBR. A round cord compresses and rebounds, it works again and again, but once flattened into a permanent set it is done. Cracks, cuts, a ring that will not compress, or fuel weeping past the groove, all mean replace. On fit, do not stretch, twist or pinch it, slip a little assembly lube on the ring and the groove to seat it, and check the ring sits in the groove without a twist. For general machine, hydraulic and fuel line use, the size matched to the groove.

 FAQ 

Q1: What size is this O ring?

19 mm inner diameter, 24 mm outer diameter, 2.5 mm cord, written as ID19 OD24 CS2.5. For an O ring the size is the part number, so measure your groove or old ring and match the ID and the cord.

Q2: What material is it?

NBR, nitrile butadiene rubber, the standard O ring material. It resists oil, fuel and heat and holds its elasticity, so it suits general machine, hydraulic and fuel line seals.

Q3: How do I know it needs replacing?

Cracks, cuts, a ring that has hardened and will not compress, one flattened into a permanent set that will not rebound, or fuel weeping past the groove. Swap it before it drags the whole seal down.