Jim-
I'm the one who called you after having my left front wheel seperate from the car at speed. Even though all four studs pulled from the Brembo rotor I decided to look outside of just a possible rotor failure. A Brembo rotor for a first gen RX-7 has 18mm available for stud thread engagement. Most studs available from the RX-7 aftermarket world have only 9mm of engagement and the unthreaded area of the stud is so small that you can keep threading the stud in past this area thereby damaging your rotor threads. They also cannot provide any specs for there studs.
I have talked with my fellow PRO-7 racers here in the Pacific Northwest, numerous engineers, engineers from ARP and Maryland Metrics and local machininsts. Finding a double ended stud with 18mm of engagement is very difficult. I ended up purchasing 12mm X 1.5 studs from Turner Motorsports. They are 75mm long with 13mm of engagement and 12mm of unthreaded area which is perfect for a 1/2" wheel spacer. Another racer is awaiting studs from Maryland metric which have 24mm of engagement. I will look at these also.
Most likely I will run the Turner Motorsport studs with my current batch of inspected Brembo rotors next season and keep a close eye on this new set up. I appreciate the help Jim.
Duane