Generally when there are notches on the fittings it is an indication of them being metric. I am going to evacuate system for verification next week to verify but wondering if anybody has confirmation that up to 91 GM did use all standard fittings in ac lines. My lines have notches, but I believe it should have standard threads and so does one of the ac places I have called. In short, I was going to order some adapters so I can have minimal down time, but these notches threw me off. Changes my down time by few days just to verify the thread size.