This is actually all about making a small chuck to grip the head of the rivet so that I could apply a torque and cut a thread with a die.
The concave dish is important as this grips the domed head of the rivet
The rivet balancing on the anvil side of the chuck
The number goes over the shaft of the rivet and clamps the head against the concave form in the anvil side of the chuck.
I can then apply enough torque to cut the thread using a die.
The interesting bit is that these rivets are just 1/16 inch and the thread is 10BA.