I see a lot of people asking what to use, cool ideas as well to avoid purchasing an expensive allen key or socket, but I'm big on the right tool for the job. I had this for my last bike. Doesnt fit Speedy.
Says it fits Triumph. 22mm - should fit Speedy perfectly. We make O2 sensor shells from 22mm hex bar stock, I just use one of the left over bar ends. $0