This is a mount for the Standard/Horizon marine radio remote mic (CMP23). It provides a way to mount the mic on the binnacle stand (pipe) when combined with a third-party rail mount. This helps avoid drilling holes and taking up space in your NavPod.

https://www.catalinadirect.com/shop-by-boat/catalina-350/hull-deck/cockpit/snap-on-railmount-stainless-steel/