Fun fact: There are plenty of times a screw that looks like a Philips head is also compatible with a square drive. I’ve mostly seen this on electrical outlets and Ikea furniture.
I don’t know why Robertson/square drives aren’t more common. They’re stable and they resist stripping and rounding.
Robertson is the proto-torxs. It is a vast improvement over Phillips but has a tendency to snap the head off due to the increased amount of torque you can apply. Torxs maintains the amount of torque that a Robertson can apply, but adds some material back to the head giving it a little extra strength.
It’s really unfortunate that the greed of Robertson and Ford got in the way of such a vastly superior design.
Phillips strips way, way easier than Torx. Stripping generally happens when a screwdriver cams out, or pops out of the screw. Here are some excerpts from Wikipedia of Torx vs Phillips.
The hexalobular socket screw drive, often referred to by the original proprietary brand name Torx ( /ˈtɔːrks/) or by the alternative generic name star drive, uses a star-shaped recess in the fastener with six rounded points. It was designed to permit increased torque transfer from the driver to the bit compared to other drive systems. The drive was developed in 1967[44] by Camcar Textron.[45] Torx is very popular in the automotive and electronics industries because of resistance to cam out, and extended bit life, as well as reduced operator fatigue by minimizing the need to bear down on the drive tool to prevent cam out.
And Philips on the other hand:
The Phillips screwdriver design has a tendency to cam out during operation due to angled contact surfaces which create an axial force pushing the driver out of the recess as torque is applied. Despite popular belief,[2] there is no clear evidence that this was a deliberate design feature. When the original patent application was filed in 1933, the inventors described the key objectives as providing a screw head recess that (a) may be produced by a simple punching operation and which (b) is adapted for firm engagement with a driving tool with “no tendency of the driver to cam out”.
I’m not sure about Allen. It doesn’t cam out very much, but it does still strip a lot easier than Torx. Probably due to the smaller contact points.
And with the hex/Allen, it’s the small contact points as well as the smaller volume of material that needs to be deformed or removed before slippage can occur, as well as the angle of force on the contact point.
With a hex, the contact point and direction are such that the tool is effectively trying to scrape off material at an angle, and if/when it succeeds even a little bit, it’s now much more prone to fail.
With a Torx, the contact area might still be small, but it’s being applied to the lobe in a more perpendicular direction, so rather than a scraping failure, it’s more of a force that is pushing directly against steel instead of scraping. Not that it can’t fail, but the route to failure is significantly less likely.
Yeah, it was made with torque in mind (like, it’s in the name lol). For smaller screws using an impact, you can expect to break the screw before you strip the torx on top. And by smaller I don’t mean tiny, more like M4, M5
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