What is this bolt/nut thing and where can I get it in Ti ?

[11.4]

Sorry, I seem to have missed where it says what it's for. Looks like the inset nut for mounting brake calipers. Tell us what it is being used for and I'm sure there's someone who makes a custom ti one for lightweight bikes.

[prendrefeu]

It's a recessed nut, by definition. Recessed nuts are used on mounting brake calipers - however the standard for that is completely different from the one in hand. The one in hand has a female m5 thread (the brake caliper variety is m6) and it's much shorter. The closest spotted so far is the 3T package with accompanying bolts (which I don't need).

On an integrated handlebar there's only one area where there is a bolt: the stem to steerer clamp area. On two different integrated bars they were designed without threaded bonded into the carbon, instead they use a recessed female nut mating to a male bolt on the other side...

[Georgezimtamwe]

Recessed brake nut:
http://www.biketweaks.com/titanium-bolt ... -nut-m6X10

But yours looks even smaller than 10mm