These are used in conjunction with a distribution dripper ends when running a length of drip line with multiple drippers beyond a single sensor. This is a very efficient and cost effective method of 

Distribution drippers can be used to increase the water delivered off of one Tropf-Blumat sensor or Maxi sensor. This will allow you to configure your water over longer planting beds, or when you want to encircle a plant around its perimeter. The savings over using multiple sensors are obvious.

Using this approach, you can run no more than 40" of line beyond the sensor, however you can only do this on a pressurised system that has ideally, a minimum of 4.5 psi. Obviously, the pressure of the system will impact how many drippers you can put on one sensor. Adjusting the black screw caps allows you to adjust each dripper to accommodate all that are on the one line. It is possible to achieve as many as 25 drippers beyond the sensor with this approach, with each dripper delivering water to approximately a 20 mm [8"] wide area.