A MUST USE tool when changing more rigid tires.
The Drop Center Tool is used to push the bead down into the center of the wheel which helps mounting and demounting tires (especially with low profile side walls). Made of plastic, it is very sturdy and will not scratch or damage the wheels.
In case of stiff sidewall tires at least two drop center tools must be used to force the tire into the drop center opposite from where the duck head is operating.