The smallest Torx size is a T1 (or TX1, whatever)! This size is best described as "pray that you never have to use it". I think I did... once... or maybe that was just staring at the driver wondering what it's for. Still, we have 16 different Torx sizes around here. Sixteen!
Also, there's a thing called Torx Plus out there. You can buy Torx Plus screws and things will work out for you, but don't buy Torx Plus bits unless you know what you're doing. That said, if you do use Torx Plus bits with Torx Plus screws, it works really well.
Off the top of my head there's TORX / tamper resistant TORX, TORX Plus, tamper resistant TORX Plus, whatever the external/female variant is called. TR TORX simply has a pin in the middle of the head, but TR TORX+ has five lobes versus six.
TORX Plus has made its rounds on the automotive circuit. It's designed to be somewhat backwards compatible but it is a lot easier to damage the fastener with a normal TORX driver.
That side note problem surely ranks as the #1 downside of torx. The practical solution seems to lie in restricting torx sizes to a much smaller subset, e.g. jump right up to T25 if T10 isn't enough (I think some fields actually do this?). But if you have the full set of drivers you can still mess up, no doubt.
I wonder if the pin/hole tolerances of the "tamper proof" variants are tight enough to keep the slightly smaller out? Then it's not so much about keeping out people who don't own the right tools (gatekeeping) but about keeping out hands that happen to not hold the right tool at the moment, which is very well possible even if one should know better, and the right tool is available as well. You should never blame the user for a mistake that could have been prevented by better UI.
the secure/tamperproof torx are fine, actually;
sometimes all screws are T15, and during a repair one of them has become T20 (embiggen the hole and what not). Preventing user errors in such cases is important, indeed.
> Side note: mistakenly using a smaller torx driver demolishes both the screw head and the driver... and it usually fits well.
Ahh yes, I learned this the hard way. T20 bit for a T25 screw, for example. It might work for a few screws then all of a sudden the next one gets destroyed.
The smallest Torx size is a T1 (or TX1, whatever)! This size is best described as "pray that you never have to use it". I think I did... once... or maybe that was just staring at the driver wondering what it's for. Still, we have 16 different Torx sizes around here. Sixteen!
Also, there's a thing called Torx Plus out there. You can buy Torx Plus screws and things will work out for you, but don't buy Torx Plus bits unless you know what you're doing. That said, if you do use Torx Plus bits with Torx Plus screws, it works really well.