The tolerance established in this part for the dimension specified as “distance between heads” shall be applied as follows on the various types of barrels in use:

(a) When a barrel or subdivision thereof has two heads, the tolerance shall be applied to the distance between the inside surfaces of the heads and perpendicular to them.

(b) When a barrel or subdivision thereof has but one head and a croze ring or other means for the insertion of a head, such as an inside hoop, etc., at the opposite end, the tolerance shall be applied to the distance from the inside surface of the bottom head and perpendicular to it to the inside edge of the croze ring, or to a point where the inside surface of a head would come were such head inserted in the barrel.

(c) When a barrel or subdivision thereof has but one head and no croze ring or other means for the insertion of a head, such as an inside hoop, etc., at the opposite end, the tolerance shall be applied to the distance from the inside surface of the bottom head and perpendicular to it to a point 11⁄8 inches from the opposite end of the staves in the case of a barrel or a 3⁄4 barrel, and to a point 1 inch or 7⁄8 inch from the opposite end of the staves in the case of the 1⁄2 barrel and 1⁄3 barrel, respectively. When a barrel or subdivision thereof has been manufactured with but one head and no croze ring or other means for the insertion of a head at the opposite end, and it is desired to insert a second head, the croze ring shall be so cut that the inside edge shall not be more than 11⁄8 inches from the end of the staves in the case of a barrel or 3⁄4 barrel or not more than 1 inch or 7⁄8 inch from the end of the staves in the case of the 1⁄2 barrel and 1⁄3 barrel, respectively, or the other means shall be so adjusted that the inside surface of the head when inserted shall not exceed these distances from the end of the staves.