27 CFR 19.283: When gauges are required.

The proprietor must gauge spirits, wine, and alcoholic flavoring materials when required to do so by the appropriate TTB officer or when the spirits, wine, or flavoring materials are:

(a) Produced and entered for deposit;

(b) Filled into packages from storage tanks;

(c) Transferred or received in bond;

(d) Transferred between operational accounts;

(e) Mixed in the manufacture of a distilled spirits product;

(f) Mingled under § 19.329;

(g) Reduced in proof before bottling;

(h) Voluntarily destroyed;

(i) Removed or withdrawn from bond;

(j) Tax determined;

(k) Returned to bond; or

(l) Denatured.