John Guest/W4 Straight Reducer - 15mm to 12mm
This adaptor lets you connect a 15mm semi-rigid pipe to a 12mm semi-rigid pipe.
It can also be used where you have a pump, shower or heater where they may come pre-fitted with 15mm straight brass tails, but you're then running 12mm semi-rigid piping (or the same in reverse)
JG Part Number: PPM201512W