Which fitting uses an o-ring to help seal its joint?

The fitting that utilizes an o-ring to aid in sealing its joint is indeed the compression fitting. Compression fittings are designed with an o-ring, which is a circular sealing element that is placed in a groove within the fitting. When the compression nut is tightened, it compresses the o-ring against the pipe and the fitting, creating a secure seal that prevents leaks of fluids or gases.

In contrast, flare fittings seal by creating a tight connection between two metal surfaces that are machined to a specific angle, requiring no additional sealing elements like o-rings. Solder fittings rely on melted solder to create a joint and do not use any additional sealing mechanisms. Threaded fittings use threads on their surfaces to create a mechanical seal, and while they can sometimes include sealing compounds or tape, they do not fundamentally depend on o-rings for their sealing efficacy. Understanding these distinctions is crucial for selecting the appropriate fitting type for different applications in refrigeration systems and piping.