I noticed the diameter seemed to be about 3/4 to 13/16".
That's the typical size for std. & HD 1/2" nuts.
That's got me thinking--
Maybe a "longer" 1/2" bolt with 2 nuts threaded on.
Drive the bolt head in and then use the "inner" of the 2 nuts to remove, hoping it jams tight against the outer nut and turns the bolt???