These are 4 litres per hour constant flow drippers.  The dripper is inserted into the side of the main 13mm or 19mm line we sell a hole punch for this. the outlet is 5mm for micro tube to lead the drip to the plant.  Used by professionals.

Of course the dripper can just be inserted into the side of the larger tube and be allowed to drip where it lies.  However 5mm tube may be pushed over the outlet and the drip taken up the side of a pot (use a pot stake to secure the tube), or taken to a distant plant. (see main photo).