This Vintage Air Stainless Steel #6 Tite Fit Nut is designed to be used in conjunction with 36400-MPA Stainless O-ring Weld-on Line End #6 which gets welded or silver soldered onto 5/16" OD Stainless Tubing. Nothing says "Attention To Detail" quite like custom Stainless Steel A/C hard lines in your engine bay.