Reddit reviews Micro 100 IT-180500 Right Hand 60° Internal Single Point Threading Tool, 0.180" Minimum Minor Diameter, 0.040" Projection, 0.500" Maximum Bore Depth, 0.023" Offset Point, 18 to 76 Threads per Inch, 0.2500" Shank Diameter, 2.5" Overall Length, Solid Carbide Tool

There are smaller internal threading tools, I have seen ones that hold carbides down to 5mm, but with everything they are still around 1/4" minimum hole size. You can also find some from thinbit.com, they have a line called microbit that can get really small, from their website "For internal diameters of .077" and larger. ". Amazon has some of them like https://www.amazon.com/MICROBIT-Uncoated-Carbide-Threading-Elliptical/dp/B01MTIZ8W3 and the price isn't horrible, but be careful to follow the recommended feed and speed suggestions, would hate to break one. If you search "thinbit" you can find other offerings too.

One other option is cut an external thread and make a tap that matches what you want and tap the hole.

If you make your own, a good reference is https://sct-usa.com/wp-content/uploads/2015/08/Catalog2015_081015_QUALIFIEDTHREADTOOLS.pdf, this is also an option instead of the microbits above, but I haven't seen prices of these tools.

OK, going to leave the above info, but was looking around Amazon and found the "Micro 100" line, search for "Micro 100 single point", the price is right, and you can get a good selection of sizes. I think this might be the way to go. Here is an example https://www.amazon.com/Micro-100-Internal-Threading-Projection/dp/B00Q8M1HQ0 but look around to get what fits your needs best.

Thanks for the question, I have ordered a couple of the Micro 100 ones to try out, as I hadn't seen them before and they look really nice for the job.