Rubber elbow & clips. Alde rubber connectors are made from EPDM rubber, tested and used in central heating systems for over a decade. Compatible with the 22mm aluminium heating circuit, tube can be fitted to the rubber by hand. Always ensure there is at least 30mm of tube inside the rubber connector, and a fitted spring clip, for the heating circuit to be watertight. Reference/Manufacturer Number: 1900-523.