Variables Used

T0 The temperature of the rod at x = 0
T(x) The temperature of the rod as a function of x
Tenv The temperature of the air, room temperature
Theta(x) The "excess" of the temperature above room temperature.  T(x) - Tenv
SA The cross sectional area
C The circumference of the rod
k The thermal conductivity of the material of the rod
h The surface coefficient of heat transfer between the rod and its environment

Heat Conduction in the Steady State