1/4" Tubing Retainer Collet used with Microline and similar "quick connect" RO manifolds and fittings.
This is the locking ring that holds the tubing in place.
This is the gripping ring used with Microline Systems and other John Guest type fittings.
Recommend also purchasing the 1/4" o-ring, PN S14EPR
Also for Reference see = How to "Use" the Quick Connect Fittings