There is a plate that attaches to the rod holder (not shown in photo) which allows the rod holder to be removed from the rail clamp. The plate is the exact same size as the clamp so there is no overhang and it is a clean look.  The plate attaches to the rail clamp with countersunk screws for a clean look. 

Available in 1-5/8", 1-7/8", 2" and 2-3/8".