The clamps were made from a short piece of 1" round aluminum stock cut down to about 1/2", but leaving a 1/8" thick, 3/4" diameter shoulder, with a 1/4" (the size of the return line) hole drilled through it, and cut in halves.  The shoulders were ground so that they fit into the slots in the stock plastic fitting.   Compare the aluminum clamp pieces with the stock plastic retainer clip.