Constituent model of extremal non-BPS black holes

We interpret extremal non-BPS black holes in four dimensions as threshold bound states of four 1/2-BPS constituents. We verify the no-force condition for each of the primitive constituents in the probe approximation. Our computations are for a seed solution with (D0) over bar - D4 charges and equal B-fields, but symmetries extend the result to any U-dual frame. We make the constituent model for the D0 - D6 system explicit, and also discuss a duality frame where the constituents are D3 branes at angles. We demonstrate stability of the constituent model in the weak coupling description of the constituent D-branes. We discuss the relation between the BPS and non-BPS branches of configuration space.