A backnut is a female threaded nut that is designed to thread onto a male threaded (either manually threaded or moulded) piece of PVC pipe or pipe fitting. Ostensibly, the nut is used to hold a flange in place through a tank wall, but can be used for other purposes.

What size is a Backnut?

Most tap backnuts will have a BSP measurement of 1/2 inch or 3/4 inch and an AF measurement of either 27mm and 32mm. So, as long as your basin wrench can accommodate nuts of 27mm or 32mm, you should be fine.

What is a back nut box spanner?

Tap back nut box spanner which is double ended, for quick assembly of tap back nuts on basins.