Which of the following is NOT a type of permanent fastener?

The correct answer is that an adjustable lock fastener is not a type of permanent fastener. Permanent fasteners are designed to create a permanent joint that cannot be easily disassembled without damaging the materials being joined. Examples of permanent fasteners include plain fasteners, raised cross fasteners, and dimpled fasteners, all of which are typically used in applications where a durable, long-lasting bond is necessary.

An adjustable lock fastener, however, is designed to allow for adjustments and is often used in applications where the fit may need to be modified or where disassembly is required for maintenance or repair. This makes it fundamentally different from permanent fasteners, which are intended to be permanent and immovable once installed. Understanding the types and applications of fasteners is crucial for structural mechanics, as the choice of fastener can significantly impact the integrity and functionality of aircraft structures.