This is our Union 316 Stainless Steel Lock fitting for 3/8" OD 304 or 316 stainless steel tube.
They are a 7-piece fitting (no special tools for assembly) consisting of 2 back ferrules, 2 front ferrules, 2 nuts and a body; the 2 ferrules seal tightly around the tube wall. They are compatible with other more expensive stainless Lok style fittings. Common sizes are listed other sizes available upon request.