These black rubber hoses are for connecting propane cylinders to a regulator. These are referred to as pigtails. They have both a Cylinder connection and regulator connection factory fitted and tested at either end. Pigtail hoses do not have a time limited in-service life however it is essential that the hose and end connections are regularly inspected and replaced if showing signs of either Visible damage, Environmental deterioration or Blistering & corrosion of end fittings. It is recommended to replace them every 5 years.