This blind filter is used for backflushing on more expensive espresso machines that have a pressure release mechanism. It fits into the filter handle in place of the standard coffee filter. Opening the flow of water from the group head causes the blind filter to fill with water and an increase in pressure which, when the flow of water is closed off, is released through the pressure release mechanism. This action should be repeated several times to flush out all the coffee residues. It is recommended that you perform this procedure at the end of each day. Depending on how often the espresso machine is used you should add a cleaning tablet or powder to the blind filter at the start of this procedure and wait for about 30 seconds between each backflush to allow time for the cleaning tablet or powder to dissolve and for it to deal with the coffee residues. We would recommend using a cleaning tablet or powder every 30 uses or at least once a week.
Please check that the diameter is correct for your espresso machine.