A bottle/glass maker term for a relatively narrow, horizontal ring on the neck of a bottle (Illinois Glass Co. 1906, 1920, 1926).  It appears that this feature was purely decorative in nature.  A ball neck is illustrated to the right on a 1875 to 1885 hair dye bottle which is described on the Household (non-food) Typology page

) actually formed a thin membrane or shelf of glass that adhered to three sides of the bottle - the two wide sides and one narrow side.  Sometime after the glass cooled and hardened, much of the thin membrane broke (the right side of the flaw) leaving a relatively thick strand still remaining which bridges between the two wider bottle sides.  In th [..]