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Most DIY-ers will have experienced the frustration of self-inflicted screw damage due to the use of the wrong screwdriver type (or size, but let's keep that factor out of this particular question).

My research thus far indicates that the key difference between Phillips and Pozidriv screwdrivers is the fact that Phillips drivers are designed to "torque out" of the screw head if over-torqued, which increases the likelihood of material damage and distortion to both screw head and driver. Pozidriv, on the other hand, is designed such that it cannot jump out if over-torqued.

The same source mentions the both screwdriver and head should be of the same type:

Phillips drivers should not be used with Posidriv screws (and vice versa) as they tend to ride out of the recess and round the corners of both the tool and screw recess.

While I can understand this for the Phillips screwdriver on a Pozidriv head, I struggle to see why this would be an issue for the reverse combination, since the risk of torque-out is absent and the screw head groove geometry appears to be quite similar.

Here is a side-by-side comparison of the two driver types (Phillips left, Pozidriv right):

Phillips vs. Pozidriv

  • It looks like there are some significant differences in the design. s1212.photobucket.com/user/rsn-mk1/media/rsn%20blog/… – David Winslow Aug 7 '15 at 13:39
  • I have been using a hand held Stanley No.1 Pozidriv screwdriver on various size Phillips head screws for years now and found that it works very well, in fact better and tighter than a Phillips screwdriver in some cases.. – Chris Nelson May 14 '18 at 15:43
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The Pozidriv screw is an advanced version of the Phillips screw but the key difference is that:

  • Phillips drivers have an intentional angle on the flanks and rounded corners so they will cam out of the slot before a power tool will twist off the screw head. The Pozidriv screws and drivers have straight sided flanks.
  • In the Pozidriv ,each the arms of the cross are parallel-sided with the Pozidriv, and tapered with the Phillips.(refer the below image , look at the space between the arms)

    Ignore the spelling mistake on Posidriv

This design is intended to decrease the likelihood that the Pozidriv screwdriver will slip out, provide a greater driving surface, and decrease wear

As you state , Phillips screwdrivers will fit in and turn Pozidriv screws, but will cam out if enough torque is applied, and chances of damaging the screw head.

BUT.

The marker lines on a Pozidriv screwdriver will not fit a Phillips screw correctly, and are likely to tear out or warp (slippage is also possible if the screw is relativity new and not subjected to corrosion)the screw head.

Meaning, if you use a Phillips on a posidriv you have greater chances of slippage.

But if you use a posidriv on a Phillips it will shred the screw head and always slippage is better than destroying the screw thus you can at least try the former if you have no proper tool kit.

The above is the only main disadvantage of the posidriv head , its very similar to look as the Phillips and unaware users end up with damaged/warped screw head.

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