Adjustable metering servovalve for a fuel injector

The metering servovalve comprises a valve body, an open/close element and an electromagnet, and is housed in a casing of the injector. The electromagnet actuates a mobile armature for a travel defined by a polar surface of the core of the electromagnet. This latter is fixed in the casing by means of a threaded ring nut, with the interposition of at least one deformable adjustment shim. The ring nut is screwed with a pre-set tightening torque on a thread of the casing so as to bring about an elastic deformation of the adjustment shim and to prevent accidental unscrewing of the ring nut. The adjustment shim is constituted by a metal ring with a cross section having a shape chosen between L, C, S, Z, and Σ.