ODS (Outside Diameter Solder) fittings are the standard for permanent refrigerant line connections in HVACR systems. The fitting consists of a brass or copper body machined to accept a refrigerant copper tube of a specific outside diameter — the tube is inserted into the fitting up to a built-in stop, then brazed in place with a high-temperature silver-bearing or copper-phosphorus brazing alloy. The result is a permanent, leak-tight joint that performs at refrigerant system pressures and temperatures for the life of the system.
Unlike flare connections (which are mechanically disassembled for service) and unlike Rotolock connections (which use gaskets or O-rings), brazed ODS joints are not intended for routine disassembly. Once brazed, the joint is essentially permanent — to remove a component connected by ODS fittings, the joint must be unbrazed by reheating to the brazing temperature, or the tube must be cut and a new fitting installed during reassembly. This makes ODS connections appropriate for the parts of an HVACR system that don't need service access, such as line set runs between indoor and outdoor units, evaporator and condenser coil connections, and any branch lines that don't include service points.
The ODS fitting family covers the same geometry range as other refrigerant fitting systems. Couplings join two ODS-prepared tubing ends. Reducing couplings step between tube sizes. Elbows in 90° and 45° change direction. Tees branch one line into two. ODS-to-male-flare and ODS-to-female-flare adapters allow transition between brazed and mechanically-connected sections of the same system.
Materials are typically wrought copper (for fittings used entirely with copper tubing) or C36000 brass (for transitions to other connection types). The internal flow passages are sized to match the equivalent tubing IDs, minimizing pressure drop across the fitting.