The present invention relates to an adaptor for a BTE hearing aid with a housing to be worn behind the ear, an earpiece for insertion in the earcanal, and a signal transmission member for transmission of a signal from the housing at a first end of the member to the earpiece at a second end of the member, the signal transmission member having a connector at the first end, wherein the housing and the connector of the signal transmission member are not adapted for mutual mechanical interconnection, wherein the adaptor has a first end that is geometrically adapted for mechanical connection with the connector of the signal transmission member and a second end that is geometrically adapted for mechanical connection with the housing, so that the signal transmission member and the housing can be mechanically interconnected through the adaptor whereby the variety of signal transmission member units to be kept in stock by a hearing aid dispenser is substantially minimized.