A coupling for an irrigation system may have a first member and a second member, each of which has threads that engage a threaded fitting of an adjacent component. The first member may have a shank and a flange that has a greater exterior dimension than the shank. The flange may have a first locking extension. The second member may have a bore that receives the shank such that the second member is slidable along the base member between a locked configuration in which rotation of the second member about the centerline induces rotation of the base member about the centerline, and an unlocked configuration, in which the second member is rotatable about the centerline independently of rotation of the base member. The second member may further have a first recess that receives the first locking extension in the locked configuration.
