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The paper is focused on the fatigue crack growth process observed in fullscale conical threaded tool joints (TJ) employed to connect the components (DrillCollars (DC), Drill Pipes (DP), Heavy Wall Drill Pipes (HWDP)) of oil drillingbatteries. Fatigue is surely the most common failure mechanism for such components.Several full scale tests have been conduced under alternating bending conditions on TJof two different sizes. Then, different FM models were applied in order to analyse theStress Intensity Factor distribution along the crack front. The material fatigue crackgrowth curve was independently determined, based on the results obtained by standardCT specimen, extracted from the component. Such FCG curves were employed, togetherwith FM analysis to predict the crack growth rate and shape evolution in the full scalecomponents, showing fairly good agreement with experimental results.