The Garmin Descent T1 & T2 Transmitter should always be installed using either a flow restrictor or an air spool, both included with this kit. Which one is used depends on the method of installation. The flow restrictor should be installed on a transmitter when it is attached directly to the high pressure port on a first stage regulator. When the transmitter is attached to a high pressure hose, the air spool should be used. Using the transmitter without either the flow restrictor or air spool could result in serious injury or death from an air pressurization failure. Both are included in this product, and are replacements for the one included with the Garmin Descent Transmitter package. Refer to the Garmin Descent Transmitter Manual for more details.