This joiner uses compression to make the joint between two lengths of MDPE pipe. Made from tough and long-lasting polypropylene, our MDPE fittings utilise an acetal grip ring and a Nitrile rubber O ring.Pipe liners (or stiffeners as they are sometimes called) should always be used with this type of fitting.It is good practise to always try and minimise the amount of joints used on any MDPE water installation wherever possible.This fitting is WRAS approved. All of our MDPE fittings can be used on either blue (potable) MDPE pipe or black (non-potable) MDPE pipe.