Kodak
Kodak Rapid Fixer, Solutions A & B for Black & White Film & Paper - Makes 1 Gallon for Film/ 2 Gallons for Paper
$21.99
Heico Hardener Part B for NH-5 Fixer is for the photographer who wishes to regulate the hardener himself should use NH-5 with this hardener.
A hardener is sometimes used in the fixing of film, in order to "harden the emulsion to the base of the film".