I suppose this may be an old trick to a few or more here but remembered something I would occasionally do working on a transmission if the bolt was rounded off.
Before someone came out with those great internally splined bolt extractors, we would just drive on a smaller 12 point socket and unscrew it that way.
So, it just so happens that a 12 point 1/4" drive 9/32" socket was the perfect fit after going thru my supply of nipple wrenches.
Thanks to Track of the Wolf for having the right size nipples.