I saw these on a set of remanufactured calipers once upon a time, and decided to try making my own. I fabricated them out of a piece of aluminum stock that I milled down to 4mm thick, which is exactly the difference in rotor thickness (duh). I even machined the o-ring recess in one side like the caliper has. Longer bolts to secure the two halves are required also. Not necessarily a cost effective process, but it worked fine with zero leaks or other issues. Been running them for about 2 years now, kinda forgot they were even on the car.
