The Gaslow stainless 21.8LH 3.00 metre regulator hose 01-6037-SS is for connecting between a butane 4.5kg cylinder or Gaslow cylinder and the 30mbar regulator. Gaslow give this hose a 20 year warranty.
This hose can also be used from your 30mbar regulator to any one of the Gaslow Cylinder Adapters to convert to a different style gas bottle fitting.
The Rubber washers in the regulator hose should be replaced every 2-3 years, which is an item that should be checked during a service on your vehicle. The washers are not covered under the hoses 20 year warranty.