What may be a characteristic of a bolt head for added security?

A bolt head that is drilled to lock wire provides a significant characteristic for added security. This feature allows for the effective use of lock wiring, which is a safety mechanism that prevents the bolt from loosening due to vibration or other forces encountered during operation. When the bolt is locked in place using wire, it ensures that the bolt remains securely fastened, which is crucial in aerospace applications where mechanical integrity is essential for safety.

In contrast, other options do not enhance security in the same manner. A hollowed-out bolt head might reduce the strength of the bolt, rendering it less secure. A bolt made of plastic is typically not suitable for high-stress environments, as plastic lacks the necessary strength and durability found in metals. Painting a bolt for visibility may aid in identifying the bolt but does not contribute to its security or locking mechanisms. Thus, the characteristic of being drilled to lock wire is specifically designed to enhance the reliability of the fastener under operational stresses.