A pendulum of mass m swings to amplitude angle θ. At the lowest point of swing, the TENSION in the string equals:

At the lowest point: T − mg = mv²/L (centripetal). v² at bottom = 2gL(1 − cos θ) (energy conservation from amplitude). So T = mg + 2mg(1 − cos θ) = mg(3 − 2cos θ). For θ = 60°: T = mg(3 − 1) = 2mg.