Tap Backnut Box Spanner [ 27 & 32Mm] For securing backnuts under sinks & baths Hexagonal shaped Holes for inserting a screwdriver Double ended Square Downpipe Clip 2 Pack The Easi Plumb Tap Backnut Box Spanner - 27 & 32mm is for securing backnuts under sinks, basins, and baths. The box spanner fits over the complete hexagonal section of the back nut thereby providing maximum surface contact. Holes are included on either end through which a screwdriver or similar object may pass through to provide extra leverage. This spanner features two different sizes at either end. Features Used to provide grip and mechanical advantage in applying torque to turn objects. Usually rotary fasteners, such as nuts and bolts—or keep them from turning. Spanner refers to a specialized wrench with a series of pins or tabs around the circumference. The box spanner fits over the complete hexagonal section of the back nut.