Abstract: A compression union for joining two tubing segments together in a sealing relationship. Each segment has a head and a compression shoulder, and a sealing face. A first and second nut are threadedly joined and compress the segments together. The segments pass through respective nuts. A thrust cap is adapted to be firmly clamped. It includes an axially-extending tongue fitted into a respective axial spline, so that tightening the nut together exerts only axial force on the sealing faces, and the thrust cap prevents counter-rotation of the tubing segments relative to one another.