I am piping air system with 4" sch 40 galvanized pipe by owners preference. Am having problems with hoghead threading deep enough. tryed every thing. 2 over notch 2under notch, new dies, different hoghead. Seems I have to thread it 2 to 3 times to get fittings to go on 5 or 6 rounds. It is set for tapered thread and has NPT dies. I've even tryed backing it up as far as I was comfortable. I would give great thanks to anyone with a solution to my problem. It is the first time I encountered it. Any one who has run big screw pipe knows this is truly a pipefighting job.