American Optical (A.O.)/Reichert Non-Contact Tonometer Target Bulb. Fits models NCT I and NCT II early air tonometers.
IMPORTANT NOTE: This tiny bulb mounts in a chrome plated knurled base (discontinued) which has a screw base of it's own. The whole thing is commonly thrown away by accident becuase it looks like part of the bulb!
Also see AO/Reichert NCT Fixation Bulb
.Trade-in your old A.O./Reichert NCT on one of Reichert's advanced Air Tonometers: PT100, or 7CR