Titanium fuel tank for the Reaction Control System (RCS) of the Service Module.
Helium pressurizing gas pushed against flexible bladders in the fuel and oxidizer tanks to force the weightless propellants out of the tanks.
(The bladder has been removed from this tank.)
Photos show the tank with its probe assembly installed and removed, and views of each end of the probe assembly.
Cutaway view shows placement of RCS tanks in Service Module.
Made by Bell Aerosystems Company, “TANK (N2H4/UDMH) POSITIVE EXPULSION,” dated 6/66, North American specification ME282-0008-000X
(last digit unreadable).