1-1/2 Inch BSP Plastic Flanged Backnut
Suits bath and kitchen sink wastes, also suitable for toilet cistern syphons.
Bathroom wash hand basin wastes use a smaller 1-1/4 inch thread (not compatible with this nut).
The outside diameter of the male 1-1/2" BSP thread that this nut fits onto measures 47.80 mm / 1.882"