A multi-string section milling tool has a longitudinally extending tubular body with mill carriers carrying hardened cutters that pivotally extend from a mill window in the tubular body by upward movement of a drive plunger. A downwardly biased piston mounted to the upper end of a flow tube is slidably inserted through a stationary thimble below the piston. The lower end of the flow tube is attached to a drive plunger which is pivotally attached to drive yoke links pivotally attached the mill carriers. The piston and thimble creates a pressure chamber in the milling tool. Fluid pressure in the pressure chamber moves the piston, flow tube and drive plunger upward to pivotally extend the drive yoke links and mill carriers radially outward through the mill window. Cessation of fluid pressure in the pressure chamber retracts the mill carriers.