The Kerr radius for electrons, ‘a’, has Planck’s constant, divided by c, and by ‘m’, mass. Think: angular momentum is the “pail on a string”. Classical energy radius is this, times the fine structure constant. Thus the FSC is the ratio of these two dimensions. I say the actual electron energy radius is smaller by 22.5, so it is the Kerr radius, times ALPHA, times 1/22.5. If we take it down another factor of 6, it could be a muon’s worth of energy, with the same field conformation.
Schwarzschild radius ‘m’ is called ‘geometric mass’ and similarly, the product ‘am’ is geometric angular momentum.
ALBERS-KERR energy radius is about a/3,000. Richard Feynman said every physicist should write the fine structure constant on the wall and worry about it !!! I write Planck’s constant.