Evolution of a screw
One topic I love to discuss in our DIY Divas workshops is on how the screw has evolved over the years. Think back to when the only screw used was a slotted screw. Thank goodness we have moved on from then!
Slotted screws are a pain in the butt. I cannot believe that you still buy certain accessories and fittings that are supplied with slotted screws. I mean, really, who wants to use a screwdriver anymore! Slotted screws were fine for manual applications, but as soon as the drill came along DIYers got a bit annoyed when the screwdriver bit kept slipping off the top of the screw.
When restoring or repairing old furniture you may still come across slotted screws. Do yourself a favour and use a manual screwdriver to remove these if you want to avoid getting frustrated, as a power drill/driver with slotted screwdriver bit can drive you batty.
As industry turned towards assembly lines, the need to invent a new type of screw was inevitable. Thanks to Henry H Phillips, namesake of the Phillips screw, automated industry - and DIY - was introduced to the Phillips screw. The crosshead design of a Phillips screw limits the amount of slippage when turned at high speed.
Step into the 20th century and power tools become the norm for any DIY enthusiast. Companies such as Bosch are designing power tools that are lightweight and powerful, so powerful in fact that the Phillips screw head can no longer contain the screwdriver bit, and we once again reach the stage where slippage occurs. It's time to reinvent the screw once again and the Pozidriv screw was introduced to the market.
The visible difference between a Phillips screw head and a Pozidriv screwhead is that the Pozidrive also has etchings that make it resemble a star. The manufacturing process for Pozidriv screws is slightly more complex of that of Phillips screws.
The Phillips screw head has four simple slots cut out of it, whereas in the Pozidriv each slot is the result of two machining processes at right angles. The result of this is that the arms of the cross are parallel-sided with the Pozidriv, and tapered with the Phillips. This design modification ensures a snug fit between the screwdriver bit and head of the screw at high speed.
But let's not stop there. Walk into your local Builders Warehouse and you will see that many screws - if not most - have a square head. This is commonly known as a Robertson screw and was in fact invented before the Phillips screw, by Peter L Robertson.
As high-speed power tools become the norm, it is generally accepted that a square-drive head on a screw allows for higher torque without slippage and result in far less stripping of a screw head. However, it is essential that you use the correct size Robertson bit if you want to avoid stripping the screw head.