Suunto HP Swivel Pin.

Connecting a High Pressure hose to a SPG or transmitter will require a HP swivel with o rings.  It allows the SPG or transmitter to swivel and more importantly doesn't leak your precious gas.

If you are using an Air Integrated Dive Computer you may decide that you want your transmitter on a short HP so that it is out of the way or isn't mistaken for a handle.