CMP Air Control S Handle - 1 Graphite Grey/Silver. This is a standard spa air control which allow the air going into the jets to be turned on or off by turning the S handle.
This requires a 1-3/4 hole to install. 1 inside diameter PVC pipe is glued into the bottom to attach this to the plumbing.The top cap is 2-3/4 in diameter and is round.