True or False: Holes for both protruding and flush head lockbolts require a fillet relief.

Holes for both protruding and flush head lockbolts indeed require a fillet relief. This relief is necessary to ensure that the lockbolt can fit properly and function as designed without interference from the surrounding material. The fillet relief allows for the correct installation of the fastener and ensures that load distribution is even and effective when the lockbolt is in use.

The fillet relief accounts for the transition between the fastener and the surface, particularly with the geometry of the locking mechanism. This is critical for maintaining structural integrity and enhancing the longevity of the assembly, as stress concentrations can lead to material failure if not properly managed. This requirement applies to both types of lockbolts, which is why the statement is true.