Phillips screws often slip, I think this is because the driver heads become worn, from people using the wrong sized phillips head with the wrong sized phillips screw. This means you have to push them down to hol dthe head in and twist them at the same time.Square heads also have a size to get right but even so are much easier for the children to drive in, as they rarely if ever slip, so the screw only needs to be twisted and it pulls it self in.
screw = wiri


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