The major contribution in this book is to study and investigate the effect of rotational speed, welding speed, axial force and tool pin profile on weld quality. Friction stir welds find use for structural and other fabrication industries. This book provides details of FSW equipment used and explains the effect of welding speed, rotational speed and axial force on the mechanical properties of butt joints in AA6082-T6 material of 5mm thickness for different tool profiles. Weld tensile strength was measured and influence of process parameters was assessed. The weld's microstructure in various zones was analyzed using optical microscope. Microhardness measurements were performed on the weld's cross-sections. It was observed that tensile strength increased with the increase of travel (welding) speed under constant rotational speed. Hardness decreased in weld nugget and heat affected zone. The typical weld defects in friction stir welding were also discussed. As tool profile is vital, Triflute and Taper screw thread profiled pins were designed and manufactured for trials. The appearance of the weld was studied for surface defects and found to be small in weld nugget.