The Suunto Flow Restrictor is used with the Suunto Wireless Tank Pressure Transmitter. You should remove the restrictor only for cleaning or changing scuba gear. The restrictor must be re-installed before using the transmitter again. The Suunto Flow Restrictor Transmitter Kit contains one Type A and one Type B flow restrictor. The shorter Flow Restrictor Type A is used when the Suunto transmitter is installed directly to a first-stage regulator high pressure port. The longer Flow Restrictor Type B is used when the Suunto transmitter is connected to a high pressure hose extension, with the hose attached to the first stage regulator high pressure port. The Suunto Flow Restrictor Transmitter Kit also contains a Suunto Wireless Tank Pressure Transmitter Quick Guide with installation instructions.