Abstract: A wear sensor comprising a pair of outputs for connection to an electrical detection circuit or the like and a link element connected between the outputs and positioned to be worn and broken at a given wear point, and resistor means connected between the outputs to be electrically in parallel with the link element and positioned not to be worn; the resistance of the link element being less than the resistance of the resistor means such that the resistance of the sensor as detected between the outputs will have an initial value, indicating electrical continuity with the sensor, until the sensor is worn to said given wear point and the link broken, and a further, higher value once the link has been broken.