Hi Eugene,
It looks as if you've not been sold a complete base. There should be a plastic nut to fit in the threaded hole in the middle. There is a hole through the plastic nut that the P11 wire feeds through. The strands of the wire are then splayed out over a metal washer and these are then fixed into the threaded hole with a spanner/wrench. I just wish I had a base to send you photographs.
The HF base has no built-in matching - that is taken care of by an external ATU that the P11 wire connects to. The Yeoman VHF base has an inbuilt matching unit and can be fed direct from a transceiver.
I hope that this helps,
Peter
G4DJB
