no 3 556 258 for example the indicator is enclosed in an insulating plastic such as epoxy resin as shown in fig2 through 4 which is easily cut or abraded the wear indicator 6 is designed in such a manner that when it is inserted in the hole 9 the tip of the electrical conductor 5 extends into the pad 3 for a distance corresponding to the safety limiting thickness 4 for wear as the friction lining is worn away due to friction with the disc the insulating plastic top of the wear indicator 6 shown in fig2 is worn away to expose the electrical conductor 5 which then comes into contact with the disc thus the alarm can be generated by the electrical contact between the conductor 5 and the disc connected electrically to the ground or by the opening of an electric circuit connected to conductor 5 due to the breaking and interruption of the u shaped portion of the electrical conductor 5 by the abrasion caused by the rotating disc it is desired that the portion of the electrical conductor 5 to be interrupted extend substantially normal to the direction of rotation of the disc because if the conductor 5 extends parallel to the rotation direction of the disc the conductor becomes powderized through the abrasion with the disc into copper powder which then extends along the surface of the insulating body of the indicator 6 thereby inhibiting complete.