It's a carver's screw. Check the Rockler catalog.

"DoN. Nichols" wrote in message
rvers.com...
549) Hmm ... not sure why the end is so sharp. It is obviously
designed for a wrench to grip the square at the top to tighten
it. I suspect that the two square eyes on the casting link to
arms which apply leverage to clamp something as the screw is
advanced -- but what is being held is not clear. I guess that
I will have to wait for someone who has seen one in service to
identify it.