Question: what is the difference between unf and unjf internal threads?
Answer: What is the difference between a standard Unified 1/4"-28 UNF internal thread and a Unified 1/4-28 UNJF internal thread? The 1/4"-28 UNJF is a Unified fine pitch UNJ inch thread for aerospace. ... A 3B class of fit is considered a precision internal thread with a tighter accuracy.