One client asked: Can I use a UNJF gauge to check a UNF external?

gaugestools’ answer is : NO, you can’t. UNJF thread is far different with UNF thread.

UNJ thread mainly used in aeroplane and spacecraft industry. “UNJ” the UN means United Inch thread, “J” means rounded root of external thread. UNJ thread greatly improve the Anti fatigue strength.

UNF thread is UNIFIED  NATIONAL FINE thread with 60 degree thread angle. The root is flat. but UNJ is rounded root.

So client’t can’t use a UNJF gauge to cehck a UNF external threads