Just measured a variety of different ones I have, sizes as follows, left to right: 0.79mm, 0.80mm, 0.73mm, 0.86mm, 0.79mm, 0.77mm & 0.79mm all taken at the tip and none are Omega or 'branded'
I’ve looked at the OEM Omega tips compared to a known .9, and I think they look very close in diameter. Though not measured.