Friction stir welding(FSW) is a solid state welding technique offering lucrative alternative to join difficult to weld materials. Among the different process parameter, tool geometry is a crucial factor which affects the weld. In the current investigation the effect of different geometrical aspects of FSW tool pin diameters are studied to obtain weld with better mechanical properties. To check the quality of weld it was characterized for macrostructure, microstructure, tensile strength and hardness tests. It is observed that tool pin with 6.1/5 mm diameter exhibited improvement in properties of the welded specimen.