It's a panel-mount flange-style connector with a bayonet lock — the quick-twist coupling you see on oscilloscope inputs, signal generators, and RF test gear.
The 4 GHz ceiling covers most lab-grade signal generators and spectrum analysers through the lower microwave bands; above that, you'd step up to an SMA or N-type. The solder cup termination means you hand-solder the centre conductor and braid to the cup and body — no crimp tool required, but it does take a steady hand and a clean iron for consistent RF performance. The nickel-plated brass body and silver housing colour are standard for indoor instrument panels; the flange mount with two holes gives a solid mechanical anchor against cable strain.