Wrangler front pipe plug question.

I just replaced the front pipe on my 87 Wrangler.  On the pipe, close to the
top is a port which  I am thinking is for a O2 sensor on newer Jeeps.  On
mine it just needs a bolt to plug it up.  Does anyone know the size and
thread of this port?  It seems to be a 5/8th fine thread, but I cannot find
a 5/8 bolt anywhere!  The old bolt was fused to the port, and I think I
threw it away a few weeks back.  If I had known how much trouble it would be
to find a new one, I would not have done so.

-David