Case middle/horn connection device for a watch

A method for attaching a horn to a watch case middle, a case middle/horn connection device and a case middle/horn assembly, the horn comprising a first connector and the case middle comprising a second connector having an undercut groove, the first connector cooperating with the second connector in order to attach the horn to the case middle. The method includes:a placing the first connector of the horn in contact with the second connector of the case middle such that one or more intermediate cavities are formed between the undercut groove and the first connector;a melting one portion of the horn so as to create a molten material;a filling, at least partially, the one or more intermediate cavities by displacement of the molten material; andsolidifying the molten material in order to make the horn integral with the case middle.