The 22mm Compression x 6mm and 1/2" Tee solar collector connection can be used with products like the AVG air valve which will screw strait into the 6mm port of the tee. 1/2" Immersion sleeves can also be connected through the 1/2" port on the tee
22mm is generally a European size but found in some Solar hot water collectors sold in Australia. Early Apricus systems where one of the many brands the had 22mm copper from the collector. The 22mm compression fitting union is normally used to join solar hot water collectors or attached other plumbing fitting to the collect.