Which UNC thread is specified for aluminum in the example?

• A. 1/4-20 UNC threads in aluminum
• B. 1/2-13 UNC threads in aluminum
• C. 4-40 UNC threads in aluminum
• D. 1/8-24 UNC threads in aluminum

Answer: (A)

Coarse UNC threads are preferred in aluminum because the material is softer and taps more easily, reducing the risk of cross-threading and stripping. The example specifies 1/4-20 UNC threads in aluminum, a common size that provides good thread engagement without thinning the wall excessively and is readily available from hardware suppliers. The other options would involve either a much smaller screw with a finer pitch or a larger diameter that may not fit the given hole or part geometry, making them less suitable for the scenario. So the 1/4-20 UNC thread in aluminum is the best match for the example.