  We propose a minimal model of a Coulomb coupled fermionic quantum dot thermal
diode that can act as an efficient thermal switch and exhibit complete
rectification behaviour, even in presence of a small temperature gradient.
Using two well defined dimensionless system parameters, universal
characteristics of the optimal heat current condition are identified. It is
shown to be independent of any system parameter and is obtained only at the
mean transitions point "$-0.5$", associated with the equilibrium distribution
of the two fermionic reservoirs, tacitly referred to as "$\textit{universal
magic mean}$".
