Rick, I am on my lunch hr. at work but I'll try and find the macro setting on the good camera when I get home. I suspect they are a more modern addition and am guessing that the big hole in the pine plug accepted a tapered finial, accomadating one end of the strap and the other end of the strap held behind the screw tip at the smaller diameter. But... that kind of counters having a screw tip in the first place so??
I can post other horns later if interested. Till then, I'll mention one I didnt buy, much larger with worm holes etc and higher priced, but the thing that was strange was it had a cork butt plug. I wish I would have taken a picture. That was weird,never saw or heard of cork being used before.