What Is an O-Ring?

A ring of rubber seated in a groove that seals two parts against water or air when they compress it. It is the workhorse seal inside faucet cartridges, spray heads, and garden-hose fittings. O-rings fail by hardening and cracking with age, and a failed one shows up as weeping around a joint rather than a steady drip.

Two rules cover almost every O-ring job. First, match the size exactly: diameter and thickness both. A near-miss ring either won't compress (leak) or gets pinched and torn on assembly (worse leak). Hardware stores sell assortment kits for a few dollars, but bringing the old ring to the store beats guessing from a chart.

Second, never install one dry. A thin film of silicone plumber's grease lets the ring slide into its groove instead of dragging, twisting, and tearing, which is the reason so many "new" seals leak on day one. Use only silicone-based grease on plumbing rubber; petroleum products swell and soften it.