Abstract: Muons, Inc. has designed, built, and is debugging an RF cavity under a contract with LANL which is a true pillbox 805 MHz cavity that can operate either in vacuum or up to 100 atmospheres of GH2 with replaceable end-walls (or window equivalents) that can be made of different materials (e.g. Cu, Be, ALD surfaces, coated...) with different geometries (e.g. shaped windows or grids). The cavity is bolted together for quick reconfiguration and, with modified support rails, will fit inside the LBNL 5 T solenoid.