What are common causes of screw lock?

Screw lock refers to the condition where a screw becomes tightly secured or 'locked' in place, making it difficult to remove. Each of the listed factors contributes to this phenomenon, which is why the most comprehensive answer is that all of the options are common causes of screw lock.

Corrosion can create a chemical reaction between the screw and the material it's threaded into, leading to increased friction and bonding, making it harder to unscrew. This is particularly common in environments where moisture or corrosive substances are present, as they can significantly degrade the surfaces in contact.

Torque refers to the amount of rotational force applied to the screw. When excessive torque is applied during installation, it can result in an increased gripping force, potentially causing the screw to lock in place more tightly than intended.

Mixing metric and imperial threads can result in poor fit and compatibility issues, leading to cross-threading or insufficient engagement. This can create additional friction and resistance, causing screws to lock when they are intended to be removed or adjusted.

Each of these elements independently contributes to the locking of screws, illustrating why the cumulative answer includes all of these common causes.