The three piece airlocks are a great choice for monitoring and stopping contaminants entering your fermenter.
Simple set up, just fill with pre-boiled water, or sanitiser mixture, and insert into your pre drilled hole/bung on your fermenter. The airlock creates a closed fermentation from inward contaminants. It will allow CO2 to blow off but not let any O2 or bugs into your fermenter.
Note if you are fermenting in a fridge/freezer, remember to check for moisture loss in the airlock. you will need to either fill with Ethanol Spray or Salty water to stop it from freezing or evaporating through to the chill plate of your fridge/freezer.