Yeah for this exact reason I despise torx. The last couple of cars I've owned have tonnes of torx screws, and as they rust and accumulate road grime over the years they change size. You will only be able to fit a T20 into an arch liner screw to start with, then as you turn it the rust and dirt dislodges, and it either becomes the next size up or cams out and rounds off. In weaker metals they round hilariously easily (torque wrench set to 20NM on a sump plug, torque wrench set to 7NM on a brake disc set screw).
My experience of Torx screws in high torque applications (bolting together Bosch high pressure diesel pumps) also makes them seem flawed, as the small contact area results in damage to the screw (hardened, awful to drill out, yet still round off with an almighty crack when enough pressure is applied, hence needing to drill out) or damage to the thin ends of the Torx driver itself 50% of the time.
Re:Robertson vs. Torx screw drives (2021)
by ryanbrunner on Monday July 04, 2022 @10:11AM
(#31977223)
Yeah, I haven't used Torx, but the author listed 100 sizes as a feature, and I'd strongly disagree. I think Robinson having a small number of sizes makes it extremely obvious when you're using the wrong one, and you can almost always tell the correct Robinson to use by sight alone. (the author lists 6 sizes, but in practice 100% of applications I've seen have used one of three)
Not sure how many sizes of Torz there actually are, but I have only seen T10,15,20,25,30,35,40 which is 7 sizes. I think I saw a smaller one in a precision screwdriver set next to the other weird iPhone/watch ones like tiny pentalobes. But effectively Torx for all normal applications is one of 7 sizes, with T20 and T25 being probably 95% of all wood screws for building/carpentry applications.
I wasn’t aware that there could even be a “T17” or “T31” - simply because no one would ever do it. Increments of 5 is already close enough to some times guess wrong.
In my experience appropriately sizing Philips is basically impossible unless the screw itself is marked. The #2 is way more common it seems so that helps with the default but if you know it isn’t #2 then you are screwed (har har) because many different size drivers will ‘fit’ and ‘work’.
In my experience, a problem with Torx is that it is a common mistake to use a bit one size smaller than what it should be. It will still engage just fine, but if you apply too much force, you'll destroy the bit, or head, or both. I find it a lot harder to notice when I pick the wrong size Torx bit, compared to a Philips or Pozidriv.
I have made this mistake a lot when using Torx. I have learned myself to always test a bit one size larger than what I think I need, just to be sure.