DIY, craft, materials, and such / interesting engineering around tools
Fasteners and washers
Washers
Screw drives
Philips head and Pozidriv
The Phillips screw drive (often marked PH on screw bits), designed in 1932, was once the typical variant of the cross-shaped screw.
They were designed as an improvement to flat-head (slotted) screws. Flat head would cam out fairly easily, slip, need some alignment. ...more so around smaller screws and around power tools.
Then again, phillips too will cam out fairly easily - more so if you get the wrong size, and just as easily with power tools.
...in fact a little more so than most other cross-style designs designed since.
(There is a theory this was intentional, to avoid overfastening, or save power tools / bits where there was no torque-based ratcheting, but neither of these seems true(verify))
Pozidriv (often marked PZ on screw bits), designed around 1960s, is a different design, from a different company.
Compard to PH, PZ will do a little more torque before it cams.
To this day it is often confused with PH. You can identify
- PZ bits/heads by the extra protrusions things between the four main wings
- PZ screws by marker slits between the actual slots
It seems many types of modern DIY screws are pozidriv,
though there are also modern cases that use Philips.
On using the wrong size PH or PZ
For both, size 2 seems to be most common for around-the-house screws, and sometimes a 3 for noticeably beefier screws.
On mixing PH an PZ
If you need minimal torque, then you can get away with treating PZ as PH, or PH as PZ, but neither is ideal.
- PH driver in PZ screws will loosely fit, but slip and cam out once you try to apply more torque, damaging screws and your bits.
- PZ drivers in PH screws will generally not go as deep, so also cam out more easily
https://en.wikipedia.org/wiki/List_of_screw_drives#Phillips