One client asked: “Can you use a UNF 3B gage to check UNJF 3B (internal)”, Here I give a answer, No, you can’t use a UNF 3B gage to check UNJF 3B internal threads.

Bucause UNF is fully different with UNJF.

UNF thread gauge is UNIFIED  NATIONAL FINE thread gage with 60 degree thread angle. it

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.

UNJ has rounded root, but UNF has straight root, so they are fully different