: A split archive extension. You need all parts (e.g., .001, .002, .003) in the same folder to extract the contents using 7-Zip . Likely Content Areas
: Likely a project or document identifier. The "Mic" suffix often refers to Microfiche records or Microphone technical specifications in older archives.
: There is documentation regarding the Model 880 Radiographic Projector and related test plans for industrial gamma radiography.