3x25mm, TX10
UPDATE: I ran out and went and bought another pack of 200.
My perfectly factual opinions notwithstanding, there are other factors that prevented the total dominance of Torx, and somewhat kept the flathead around.
The first is simple metallurgy. The Robertson was a direct competitor to the Phillips, but punching a deep, straight-sided square hole into the head subjected the metal to a lot more stress compared to the angled cruciform of Phillips. It made the head brittle and the screw worse overall. This is a non-issue with modern manufacturing practices, but it was a significant factor decades ago.
The second is a saying that applies to most fields of technology: standardized is better than perfect. I still groan in frustration whenever I encounter a pentalobe or tri-point screw because I never have the correct screwdrivers at hand. It was the same situation with Torx about 10-15 years ago. It proliferated since then, and all of my sets now contain several Torx bits. I believe it will overtake the Phillips with time.
(edit) I was incorrect in the first point. The original square head screw was invented in the USA and used a flat-bottomed die to stamp the recess into the head, which is what caused the brittleness. Robertson’s die has sloped walls and a bottom that tapers into a point (like a short obelisk) that mitigated this weakness somewhat. The real reason the Phillips came out on top is because Henry Ford chose it over the Robertson.
