Compression Coupling. 2-way: compression x compression. These fittings do not require any glue or clamps to connect. Simply insert hose into fitting by pushing back and forth, until you feel stop in the fitting. Select for fitting size based on tubing size. 600 (green) fits 16 mm tubing (OD= .620"), 710 (blue) fits 1/2" ID & 18 mm (.710" OD tubing), and 900 (gray) Fits 3/4" tubing (OD= .940").