Required For IEC Electrical Parts
Phillips and PoziDriv bits, despite their similar appearance, are two systems that are not interchangeable. Here's how to tell the difference between them:
The Phillips bit has a self-centering design. Phillips bits have an intentional angle on the flanks and rounded corners so they will cam out of the slot before twisting off the head. The most common Phillips sizes are 1, 2, and 3 (from smallest to largest). Phillips bits typically have "PH" indicated on them.
The PoziDriv also has a self-centering design, but the shape is modified for improved engagement. The sure sign that a screw is PoziDriv is the four slots cut into the face of the screw. A PoziDriv has ribs between each of the four arms of the cross. This adds the increased grip. The most common PoziDriv sizes are 1, 2, and 3 (from smallest to largest). PoziDriv bits typically have "PZ" indicated on them.
Note: Phillip's drivers should not be used with PoziDriv screws (and vice versa) as they tend to ride out of the recess and will damage the driver and the screw. IEC electrical parts have PoziDriv screws.