Two 16 gauge wires twisted together at both ends are roughly equivalent to one 12 gauge wire.
This may not be used for household wiring, either permanent or portable, but could be used for portable low voltage or loudspeaker wiring.
A 16 gauge wire emerging from a device such as a light fixture may be wire nutted to an 8 gauge feed wire but there is little usefulness* for this. The circuit feeding the light fixture or receptacle may not be breakered at more than 20 amps for which 12 gauge wires are sufficient.
* One use would be for a very long run, say hundreds of feet.
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