Which factor could lead to a screw lock due to improper fit?

The reason a too short thread portion could lead to a screw lock due to improper fit relates to the basic principles of fastening and load distribution in threaded connections. When the thread portion of a screw is too short, it means that there are insufficient threads engaged with the mating part to allow for proper load transfer and resistance to vibration or movement.

Inadequate thread engagement can result in a loss of mechanical strength and clamping force. As a result, the screw may not be able to resist the forces acting upon it, which can lead to a loosening effect often referred to as “screw lock.” This condition can arise in applications where vibration is present, causing the screw to loosen over time and potentially leading to a failure in the assembly.

The other factors listed may influence screw performance but do not directly relate to the fundamental issue of thread engagement that is critical for maintaining a secure fit and preventing screw lock. For example, excessive grip length may allow for additional clamping area, while excessive lubrication might affect torque but not necessarily compromise thread engagement directly. Understanding the importance of the thread portion length is essential in ensuring the reliability of threaded fasteners in aerospace applications.