RAF flying helmet receivers, type C

Stores reference 10A/7063.  'Receivers, telephone, head, type C', as used with the Type B flying helmet and Type D oxygen mask.  Manufactured in plastic/bakelite moulded over a steel shell with a separate screw-on bakelite cover.  Surface wear, scratching and knocks to main casings.  Both covers/caps are absent but most of the internal components appear complete.  Dirty with some corrosion of internal parts and the case threads.  Remarkably difficult to find now.  Stock code HC-NIV.