CMB (Made in Germany)  Pin lock disconnect fits onto your gas in keg port.

6mm barb  

The gas disconnect has a grey base (the beer out disconnect has a black base)

They easily attach to the keg post and a twist locks the collar securely. 
 A plunger in the disconnect depresses a poppet valve built into the post allowing the flow of gas or liquid. 

As the disconnect is removed a spring automatically closes the poppet valve preventing the loss of any pressure or liquid. It also prevents the ingress of any O₂ protecting the contents from oxidation.