At the time the Mercury M range was introduced a governing body had decided that 4mm Banana Plugs were unsafe because they share the same diameter as a European mains plug. After an incident involving an injury as a result of loudspeakers being plugged into a mains socket, it was decided that 4mm banana plug connections were unsafe and that all Hi-Fi equipment should have it's connections reduced to 3mm as a standard across all models. The Mercury M range was introduced during this period, however, the switch to 3mm connections never took off and the hi-fi world went back to using the standard 4mm connections not long after.