I’m a convert and no, I haven’t given up the drink and gone teetotal, rather I’ve switched allegiance from Pozidrive to Torx headed screws.
When I started woodwork many years ago, like many others, I used the traditional steel and brass countersunk slotted screws, which are excellent when driven by hand using a screwdriver where the blade fits exactly into the slot. I still use brass screws with polished heads for hinges and where the screws will show, but they’re becoming increasingly difficult to find, which is slightly irksome as, at one time, the local ironmonger in the town or village would have stocked a reasonable selection. Alas, those days are long gone.
The development of the rechargeable battery powered drill driver sounded the death knell for the traditional slotted screw as no matter how carefully they were used, the bit invariably slipped out of the slot at a crucial moment and gouged its merry way into the job.
In order to prevent this slippage, the Phillips screw, with its star shaped recess, was probably the first basic attempt at a screw head designed specifically to be driven by power. It sort of works, but suffers from the dreaded affliction of ‘cam out’ as the driving force is axial, rather than radial. This means that as the screw is driven into the wood under increasing force, there’s a tendency for the bit to slip if there’s the slightest deviation in the correct contact angle with the screw. We’ve all experienced this effect at some point when you hear that ‘rat-a-tat-tatting’ of the bit as it attempts to vainly turn the screw the last few millimetres into the wood. The immediate effect is that both the bit and screw are invariably mangled beyond redemption and both usually need to be replaced.
The Phillips head was superseded by Pozidrive which had a similar looking head and which promised to be much better, which to a certain extent, it was but…. it still suffered from ‘cam out’. Not as badly, it has to be said, but unless you’re extremely careful, you’ll still mangle bits and screws.
Clearly, the ‘star’ shape of both the Phillips and Pozidrive screws prevented the bit from slipping completely out and onto the work, but the cone shaped recess on each type meant that both the bit and screw were prone to ‘cam out’ damage.
The shape is still ‘star’ shaped, but now the driving lands in the recess are parallel to the screw shank, so that the torque applied is truly radial rather than axial and is thus transmitted far more efficiently to the screw.
The result is that the screw requires a lot less effort to drive into material, so much so that the screw head will end up several millimetres underneath the surface of the job unless you’re quite careful, but the greatest bonus is the almost complete elimination of the scourge of ‘cam out’.
I tried some of our Axminster WoodSpur Torx headed screws out in the workshop and was simply astounded at their performance.
Anyone want about 1500 Pozi screws before I bin them?