The difference between UNJF and UNF

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Cutting TapsRoll (Forming) TapsRound DiesThread Mills Unified Threads Standard (Screw Threads, Center Holes)How to useSpecification of toolsBasic Knowledge

This time I need to work on aircraft parts and I plan to produce a 1/4-28 UNJF internal thread. 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. There are other Unified UNJ threads such as UNJC coarse pitch threads and UNJEF ultra fine pitch threads. The thread accuracy is referred to as a 3B class of fit or a 2B class of fit. A 3B class of fit is considered a precision internal thread with a tighter accuracy. The 2B class of fit is considered an intermediate class of fit for an internal screw thread. The dimensions of the pilot hole diameter or minor diameter for a 3B and 2B class of fit will differ.

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