Answer:
Option A
Explanation:
Nylon retainers are knocking screws that have nylon coating on their thread which prevents them from loosening. It generally has two heads Hex Key an star screw. For high mount fixing, star screw is used as it is less prone to stripping. The nylon insert of a Nylock nuts enters into the screw and prevent it from loosening. It is useful in areas where there is high vibration.
Hence, option A is correct
