"Got this recently. I've 4 other tap backnut spanners, even the drawdropper - non of which fitted a particular tap. This boxspanner did!!
Another good use, is to put over basin tap spouts to hold the tap while tightening up the backnut (using a different spanner!), gives better leverage for those annoying taps that move as you tighten them up. wrap spout with something first to protect it though."