Tools required: safety wire and safety wire pliers (can be bought as a kit from major retailers). It's the best middle ground I've found between clip style and rivet style master links; it's by far the easiest set-up and if done right is very safe and secure. You get the convenience of the clip style with the security of the rivet style...no chain tools needed for install or removal. This sort of master link securing is done in the aviation industry.