A coupling assembly includes a fixed component and a pivotable component. The fixed component has a base and an upstanding projection with a central bore and a plurality of small apertures around the bore. The pivotable component has a distal section and a proximal section with a planar face in sliding contact with the fixed component. The pivotable component has a threaded aperture axially aligned with the bore of the fixed component. A pin in the planar face is selectively positionable in a small aperture. Intermediate components adjustably couple the fixed and pivotable components. The intermediate components include a bolt received in the threaded aperture and slidably received in the bore. The bolt has a free end extending through the bore with a nut adjacent to the free end. A coil spring on the bolt between the nut and the fixed component urges the pin into a small aperture.