I have to design a part that will have screws that can be taken apart with a T9 Torx Screwdriver. These are the screws that are taken apart first thing here. What is the thread diameter of the screw that mates with the T9 torx screw in the Metric System?

On this website they mention "point-to-point" dimensions. But I am unable to understand what that refers to.

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    If not mistaken most screwdriver sizes will fit a range of screw sizes/diameters, instead of being specific to one size only. Seems like a bad way to design a part to be based on screwdriver size.
    – crip659
    Commented Jul 18, 2022 at 13:11
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    "T9" tells you about the head of the screw. It tells you nothing about the threads.
    – brhans
    Commented Jul 18, 2022 at 13:38
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    "I want to find out the thread diameter of the screws that are on that engine". Then this is the question you should be asking, and you should probably ask in the comments section of the video, or look for a support forum for that particular car and ask there. Thread pitch/diameter are not determined by the head of the screw, the head of the screw is determined by the thread diameter.
    – FreeMan
    Commented Jul 18, 2022 at 13:43
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    There are ways to check the thread size of a screw. If you ask that question here you'll get an answer. You should explain a little more about what you are trying to achieve. Where are you and where are you going? It seems unlikely that you don't know the difference between a screw head and its thread, and yet you are designing replacement parts for jet engines.
    – jay613
    Commented Jul 18, 2022 at 14:06
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    @jay613 A bachelor's course in aerospace engineering probably fits this bill. I remember ordering my first set of M10 bolts without specifying length for example... I got a box of 10mm ones.
    – MiG
    Commented Jul 18, 2022 at 14:10

2 Answers 2


The T9 is the type of screwdriver you'll need to remove/install the screw. It's similar to saying a slotted screw or a Phillips screw. It has no bearing on the thread size. If you need the thread size, you'll have to find a blueprint of the engine or a parts list on their website.


There is NO standard for wrench size vs screw size in metric.

I checked, because it kept coming up.

In point of fact, T9 is a real oddball, there's no earthly reason they couldn't have stepped down to the more common T8, or up to the extremely common, and part of every set T10. They are doing that on purpose, to make the device non-user-serviceable.

For that matter, who's to say the machine screws are even metric? I see what looks like a Starbucks coffee, and that's definitely an L14-20 or -30 twist-lock socket in frame. That plus the accent tells me we're probably in the United States, and the screws might be standard.

Standard generally follows SAE guidelines, which do specify head size for bolt size. Show me a 1/4" bolt I'll show you a 7/16" hex. I don't think they delve into Torx, but SAE definitely would not approve of oddball sizes like T9 when a common size like T10 is right next door.

  • +1 I even checked the Chinese suppliers who make 'everything' including M2.6 which I've never even seen in real life - & they still jump from T8 to T10.
    – Tetsujin
    Commented Jul 18, 2022 at 17:44
  • @Tetsujin My Chinese cheap tools are better than yours :-) I've got T3/T4/T5/T6/T7/T8/T9/T0/T15/T20 in my latest little toolkit. But I agree it is an oddball. Commented Jul 18, 2022 at 18:11
  • @manassehkatz-Moving2Codidact - LOL. I tend to use Wiha bits, because they need replacing about once a decade or so, but they don't include the low, odd numbers, odds start at 15. ;) The bits themselves are relatively easy to find, but bolts to match them, another kettle of raspberries entirely...
    – Tetsujin
    Commented Jul 18, 2022 at 18:15
  • @Tetsujin My tools are split between the heavy duty stuff (just checked my set of DeWalt bits - also made in China, but decent quality - and they start at T15) and lots of small tools for phones/laptops/etc. (which is closer to what I actually do for a living). Commented Jul 18, 2022 at 18:18
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    @manassehkatz-Moving2Codidact - I was always 'middle ground' - multimedia installations, service & maintenance, for retail stores. Nothing huge, nothing tiny. Lots of M3 & 4 bolts… & wing nuts, for some godforsaken reason ;) …and we seemed to have a deal with some factory who made self-drillers. Killer-drillers, go through anything, usually making it non-saleable as it went through the guts of 'demo models' which were often real products destroyed by fixing them into demo stands.
    – Tetsujin
    Commented Jul 18, 2022 at 18:26

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