Bottle Cap, Adapter, This adapter will allow you to connect a 38 mm bottle cap to a 45 mm, 2.5 liter Bottle. Proligo has started shipping Acetonitrile in 2.5 liter bottles that use a slightly different 45 mm bottle cap from the standard Schott 45 mm bottle cap. Therefore if you have a device (instrument) that has 38 mm caps on it that used to fit your 4 liter Acetonitrile bottle and now you are getting your Acetonitrile in 2.5 liter bottles from Proligo, you will need this adapter.