[en] High strength to weight ratio with good corrosion resistance of aluminum alloy (AA) 7039 make it the first choice for armor plate in the defense industry. Friction Stir Welding (FSW) is a solid state welding process and used to join this aluminium alloy. In FSW process the tool design acts an vital role. In the present study, the effect of tool-pin profiles and its diameters has been evaluated on the mechanical properties of Friction Stir Welded (FSWed) joint. Four pin profiles- cylindrical, conical, triangular and square, each with three different diameters (5 mm, 6 mm and 7 mm) are used during experimentation. In microstructure analysis, a high density of fine precipitate of zinc and magnesium is observed in the welds produced with high frictional heat which caused hardening of the processed zone and also a high level of mechanical strength in the joints. Onion ring patterns are found in the joint area due to the movement of material in batches as the edges of the pin forced the material to flow under the tool shoulder at a different pace. The pulsating effect of square tool pin has produced finer and properly distributed grains in the nugget zone. The eccentricity and pulsating effect of the square pin have mixed the softened material more effectively than other pin profiles, therefore, a better quality weld was obtained. The tool pin with diameter 6 mm is found more suitable for producing joints with better properties than pin of diameters 5 mm and 7 mm as it has forced the optimum volume of material to flow in welding. High-level plastic deformation has caused a variation in grain size and dynamic recrystallization across various zones of welded joint, which has resulted in hardness gradient. (paper)