Abstract: A coupling for joining a pair of tubes having ends has a ball having a substantially spherical outer surface and a center and formed with an outwardly projecting pin extending along an axis radial of the ball and center. The pin is dimensioned to fit snugly into the end of one of the tubes. Another pin dimensioned to fit snugly into the end of the other of the tubes has a seat shaped to complementarily fit against the surface of the ball. The other pin is secured to the surface the ball at any of a multiplicity of angular offset positions thereon. A threaded bore is formed in the ball and centered on a bore axis traversing the center and another bore is formed in the other pin, opening into the seat, and centered on a bore axis extending at an acute angle to the respective pin. A screw extends through the bore of the other pin and is seated in the threaded bore of the ball. Normally the bore axis of the threaded bore extends at an acute angle to the axis of the pin of the ball.