In addition to the straight sided flanks of the Pozi screw, there are 8, not 4, of the flanks. While those additional 4 flanks can be seen in the screw head, it is more readily seen on the driver. The primary point of contact for torquing the screw is the big 4 (hence, a phillips working), the other 4 contribute to the ability to torque without the driver lifting out of the screw head
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