I knew this one! Although most people still refer to it as a fifth, the liquor industry (distilled spirits) went metric in the late 70’s (if I recall correctly), what we are getting now is a 750 ml. 750 ml is real close to a fifth, about 25.4 ounces v 25.6. Not much difference to the consumer but I imagine it amounts to many extra bottles for the producers. Also, what used to be a quart is now a liter, which is slightly larger than a quart.