Fuel injector, method for the assembly of a fuel injector and tensioning device for mounting of a fuel injector

The fuel injector (10) has an injector housing (11) provided with a nozzle body (12), which is axially tensioned by a nozzle tensioning nut (20) against a holding body (15). The nozzle tensioning nut has a collar (21) in a coupling nut. The collar lies at the nozzle body. The nozzle tensioning nut has a holding unit (30) for a tensioning device for elastic extension of the nozzle tensioning nut in longitudinal direction in a partial area between the collar and a thread hole (23). Independent claims are included for the following: (1) a method for mounting a fuel injector; and (2) a tensioning device provided with two tensioning elements.