Abstract: A coupling for swaged attachment to thin wall tubing. The coupling is a cylindrical body with a longitudinal axis and an inner peripheral wall. At least one groove is located in the inner peripheral wall. In one embodiment, the groove is substantially rectangular in cross section. The rectangular groove has a base and two side walls. The side walls meet the base to form corners. The corners have a radius of curvature of at least the depth of the groove. Alternatively, the cross section of the groove can be ramped in shape. The ramped shape groove has a base and two side walls. One of the two side walls meets the base at about 90.degree., and the second side wall meets the base at an angle substantially greater than 90.degree.. In a third embodiment of the invention, the groove is ramped with one side wall meeting the inner peripheral wall of the coupling sleeve at about 90.degree.