In the steel example, which UNF thread is specified?

• A. 1/4-28 UNF threads in steel
• B. 2-64 UNF threads in steel
• C. 1/4-28 UNF threads in titanium
• D. 1/4-28 UNC threads in steel

Answer: (A)

The fundamental idea is reading a thread designation and recognizing UNF versus UNC. UNF (Unified National Fine) denotes a finer thread pitch than UNC. In the given steel example, the size is 1/4 inch with 28 threads per inch, which is exactly a 1/4-28 UNF thread. Since the material specified is steel, the correct statement is the one that combines the UNF designation with the 1/4 inch diameter in steel.

Why the other possibilities don’t fit: a 1/4-28 UNF in titanium contradicts the steel specification, so it’s not matching the material requirement. A 1/4-28 UNC would be a coarser thread (20 TPI, not UNF). A 2-64 UNF would be a different diameter and an even finer pitch than 1/4-28, not the size described in the steel example.

So the correct choice is the 1/4-28 UNF threads in steel.