The invention relates to an adapter for operating a hole saw on a prime mover, particularly an electric hand drill, comprising a driving segment for taking up torque and a threaded segment for screwing into a threaded hole present in the hole saw, and at least one driving dog for entering a receiving hole present in the hole saw. Each of the display frames enables display of a plurality of information pieces, and a selected display frame is enlargeable, while non-selected display frames are reduced according to an enlargement ratio of the enlarged display frame. The hearing aid comprises sound generation means for generating an acoustic guiding signal to be provided for a limited period through said receiver during insertion of the ear plug part into the ear canal, in order to be applied by the hearing aid user to optimize the positioning of the ear plug part. A heater and a conductor to apply a current to the heater are formed between the passivation layers.