26awg x 4. I made this cable out of 8 strands of w2893. It wasn't too bulky either. It sleeved just fine in 550 paracord. It was tight, but still do-able.
He later decided he didn't want the mic split so I reterminated it to a single 3.5mm Canare (F2? I can't remember) and put 4 wires to each driver, I re-sleeved that with 1/4 nylon multifilament. I loved that cable.