The hollow thing looks like the piece from the end of a belt. The end tip of the leather or cloth belt would have gone inside it. I'm wearing a belt right now like this, though the metal piece is shorter.
Iím always interested in these metal detecting posts. My kids got me one for Christmas years ago. My most memorable find was a copper roof...a whole roof ( about 20 ft x 25 ft ) There wasnít any sign of the rest of the building, but the thick copper roofing was all intact. I guess if you couldnít find that, you werenít liable to find old wheat pennies.