What is the name of this Allen-head furniture fastener?
While difficult to tell for sure I think it is an E-Z Lok threaded insert. It consists of a course threaded screw that is inserted into the wood. A pilot hole is drilled and the insert is screwed in with a Allen wrench until it is flush. The center of the insert is tapped for a machine screw. The advantage of this fastener is it can be disassembled numerous times with out stripping the wood.