I've been trying to figure out the engine oil system and I've been looking at thermostats to be used in conjunction with a oil cooler. I had been looking at Improved Racing's FSM-165 which has a patent pending, hi-flow, low pressure drop design. I was about to click on the buy button when I realized that while it can be ordered with -12 AN male fittings, the female ports are just -10 AN.
@&#%! This is a problem because the manufacturer of the oil dry sump, Daily Engineering, is very specific that the pressure line (i.e., connection between the pump and the thermostat) must be -12. So, I spent a lot of time looking for a thermostat with -12 capacity all of the way through and only found one which I didn't like nearly as much as Improved Racing's.
I contacted Improved Racing and they had good news. The ID of a standard -12 AN straight hose end is 0.58" and their male fittings have an internal ID or 0.60". In addition, Improved Racing's thermostat is much less restrictive than other brands. The pictures below compare their thermostat to Mocal's, note how open their's is. In any event, the point is that even though the FSM-165 has -10 female ports it will be the least restrictive part of the -12 pressure line.