According to FNEI, tungsten gear wheels don't build into anything, unless I'm missing something.

... It's possible that this is true. it's been a while, but they did used to be used for a few things, but it is likely that most, if not all recipes were replaced with Titanium or Nitinol gear wheels.

Are there any of my mods you don't have?

Sorry for the delay. I see. I have most mods installed, except Enemies, Personal Equipment, Vehicle Equipment, Modules, and Warfare.

After doing some digging into it myself, all references to the Tungsten gear wheel have been replaced with Nitinol gear wheels.

their only remaining references are in fallback positions.
EG If nitinol gear wheel, add nitinol gear wheel, else if tungsten gear wheel, add tungsten gear wheel, else...
Since both nitinol and tungsten gear wheels are added by the same bobs mod, you'll never end up with a requirement of tungsten gear wheels.

However, the mods are made in such a way that if you were using them with a different mod (Say, DyTech, if that's even still a thing), that mod (last I checked) added a tungsten gear wheel, but no nitinol, so the recipe performing the check would fall back onto using DyTech's tungsten gear wheels.

Likewise if you were using some of DyTech's production mods with Bob's MCI, then the Tungsten Gear Wheel that you make in Bob's mods would be able to be used in DyTech.

However, for the pure bob's experience... Tungsten Gear Wheel is not used.