Abstract: An apparatus and method for determining the diameter of a measured object including a frame having a quick disconnect fitting that demountably couples to a sensor selected from a collection of different length sensors so that the measurement range for determining diameters is increased. Each different length sensor includes a sensor probe tip that is biased in an outward direction therefrom so that when a selected sensor is coupled to the quick disconnect fitting, the probe tip contacts the measured object. The sensor includes means to generate a signal indicative of its probe tip position, and a microprocessor is programmed to receive the generated signal and provide an output display that corresponds to the diameter of the measured object.