27 C.F.R. § 19.165 – Unit bonds.

(a) Unit bond covering operations and withdrawals. If a person is otherwise required to file bonds for both operations at one or more distilled spirits plants and withdrawals from one or more distilled spirits plants, the person may instead submit a single unit bond that provides all of the guarantees that would otherwise be provided by separate operations and withdrawal bonds. The unit bond may also provide coverage for operations at adjacent bonded wine cellars. For purposes of this section, a person includes a corporation, together with all of its controlled subsidiaries, and a controlled subsidiary has the same meaning as in § 19.163(b).
(b) Required penal sum—(1) General. A person must determine the penal sum for the unit bond by separately calculating in accordance with § 19.166, and then totaling, the amounts needed to cover operations and withdrawals at each individual plant covered by the bond. The penal sum for the unit bond must not be less than the sum of the minimum penal sums that would be required if each of the plants had its own bond.
(2) Allocation between operations and withdrawals. A unit bond must show separately the amount of coverage provided for operations (including operations at each adjacent bonded wine cellar if applicable) and for withdrawals at each distilled spirits plant covered by the bond.
(3) Tax liability must not exceed allocated penal sum. If the amount of the penal sum allocated to operations at, or withdrawals from, a particular plant is less than the maximum amount prescribed in § 19.166 for a single plant, the tax liability for operations at, or withdrawals from, that plant must not exceed that allocated amount.
(4) Total penal sum available for each plant. Even when the penal sum of a unit bond is allocated among multiple plants, the bond must provide that the total penal amount of the bond will be available to satisfy any liability incurred under the terms and conditions of the bond at any plant covered by the bond.
(26 U.S.C. 5173)