Aircraft bolts are usually manufactured with a

• A. Class 1 fit for the threads
• B. Class 4 fit for the threads
• C. Class 3 fit for the threads
• D. Class 2 fit for the threads

Answer: (C)

Thread fit class describes how tightly bolt and nut threads should mate, which directly affects how a joint clamps and stays secure under vibration. For aircraft bolts, you want a level of precision that gives a predictable torque-tension relationship and reliable clamping force after installation. A Class 3 fit provides a relatively tight, consistent engagement, so the bolt seats cleanly, threads mesh with little play, and the joint behaves predictably under load. It balances the need for accurate engagement with practical manufacturability and assembly; looser fits would allow more clearance and potential loosening, while far tighter fits could make assembly harder or risk galling. Hence, Class 3 is the standard choice for thread fit in aircraft bolts.