Lucas-Milhaupt Sil-Fos® Rings for brazing copper tubular components. Braze rings are easy to use, minimize waste, and provide visual verification of a complete, sound braze joint. Sil-Fos Rings are a brazing alloy composed of 15% Silver (Ag), formed into rings to fit inside the flared fitting used to join copper tubing and fittings (commonly used in HVAC/R systems). When properly heated, the rings create a tight, leak proof joint.