get a wire hanger cut it into 2 u shape pices slot them into the holes on the frunt of radio where the 4 holes are put some presure on them and pull the radio from the tape deck just did this today...
Need to know year, make and model.
In reality, it can be any size you want it to be. Traditionally, it is the size of the average cake pan, though.
Its a 30mm socket
I would guess that it depends on the model, but on a 2005 Ion 2 it is 30mm.