A case middle/horn connection device for a watch, a method for attaching an attachment piece including at least one horn to a case middle and a case middle/horn assembly. The connection device includes an attachment piece including at least one horn having a first connector and a case middle having a second connector, the first connector being configured to cooperate with the second connector to attach the attachment piece to the case middle. The first connector includes a tongue with a recess. The second connector includes a groove with an undercut portion. The undercut portion is configured to lodge inside the recess of the tongue; and the case middle and the attachment are made integral when the undercut portion of the second connector is lodged in the recess of the tongue of the first connector.