Nice simple machining job to enclose a 1.3GHz RFCI drop-in isolator (three-port circulator with a dummy load on the third port) and act as a heatspreader in case of a load fault. I had bought six RFSL2347s direct from RFCI, but only needed three. They can handle 200W CW, 1kW peak and 100W CW dissipation.
I sold two and this one was spare. I ran up a CAD design in Fusion360 to get the dimensions right, but then made it on my manual Bridgeport mill.