How much of the screw must penetrate into the material to ensure proper grip?

The correct answer indicates that for proper grip, at least two-thirds of the screw must penetrate into the material. This level of penetration is crucial because it allows for sufficient engagement between the screw threads and the surrounding material, ensuring that the fastener can hold up against pull-out forces and any other stress that may be applied. A greater percentage of screw penetration into the material enhances the frictional resistance and mechanical interlock that occurs when the screw is driven in, substantially increasing its overall strength and stability.

Penetration of two-thirds ensures that the screw's threads are deeply embedded, which is particularly important in applications where load and torque can be substantial. Insufficient penetration, as would occur with lesser amounts like one-quarter or one-half, could lead to reduced holding capacity and increase the risk of failure under load.

In construction and electrical installations, this understanding is vital for ensuring the reliability and safety of mounted electrical devices, fixtures, and raceways. It is essential to follow the manufacturer's specifications and standard practices to maintain the integrity of the assembly.