I have tried looking for the answer to this but had no luck. I am putting a GT40 intake on and I tapped the 3/8"NPTs but I needed to change the coolant hose on the back center of it and screwed up the threads taking the explorer hoses off, the intake is corroded bad. I need to tap it a little deeper to get a couple good threads to bit. I am thinking it may be a 3/4 NPT, anybody know the anwer to this.