Gang tube rail structure is attached to the lower front and rear corners of the implement gang tube to provide a lower clamp support. Two pivoting clamp jaws are attached to the clamp support and secured against the support by tightening a single clamp bolt extending between the lowermost portions of the jaws. A locator shoe is secured between the tube and the c-spring and includes a protrusion that projects into a hole in the c-spring. The ends of the locator shoe include short legs that wrap around the gang tube rail. The single clamp bolt provides a vertical clamp force that is approximately twice the tension generated in the bolt when the nut is tightened.