A system, comprising: a carrier system adapted to be worn by a user and to support at least one of a plurality of differently sized tanks (400,400', 400") of breathing gas, a pressure regulator attached to the carrier system and a connector attached to the carrier system which is in fluid connection with the at least one pressure regulator; characterized by a bracket connector attached to the carrier system; and a plurality of brackets (800,800', 800"), each of the plurality of brackets (800, 800', 800") being attachable to an associated one of the plurality of differently sized tanks (400, 400', 400") and to the bracket connector, wherein each one of the plurality of brackets (800, 800', 800") comprises a first section (800a, 800a', 800a") and a second section (800b, 800b', 800b") that is removably attachable to the first section (800a, 800a', 800a"), each one of the plurality of brackets (800, 800', 800") being attachable to the associated one of the plurality of differently sized tanks (400,400', 400") by attaching the first section (800a, 800a', 800a") to the second section (800b, 800b', 800b") to capture a portion of the associated one of the plurality of differently sized tanks (400, 400', 400") so that the tank valve (410, 410', 410") extends between the first section (800a, 800a', 800a") and the second section (800b, 800b', 800b"), and wherein, for each one of the plurality of brackets (800, 800', 800"), an assembly comprising the one of the plurality of brackets (800,800', 800' ') and the associated one of the plurality of differently sized tanks (400, 400', 400"), when attached to the bracket connector, positions the associated one of the plurality of differently sizedtanks (400, 400', 400") in a predetermined rearward position relative to the carrier system and at a predetermined height relative to the carrier system so that a distance (Dl, D2, D3) between a tank valve outlet of the tank valve (410, 410', 410") of the associated one of the plurality of differently sized tanks (400,400', 400") and the connector corresponds generally to a radius of a circular arc and varies by less than no more than 0.01270 meters (0.5 inches) for each one of the plurality of differently sized tanks (400,400', 400"). a carrier system adapted to be worn by a user and to support at least one of a plurality of differently sized tanks (400,400', 400") of breathing gas, a pressure regulator attached to the carrier system and a connector attached to the carrier system which is in fluid connection with the at least one pressure regulator; characterized by a bracket connector attached to the carrier system; and a plurality of brackets (800,800', 800"), each of the plurality of brackets (800, 800', 800") being attachable to an associated one of the plurality of differently sized tanks (400, 400', 400") and to the bracket connector, wherein each one of the plurality of brackets (800, 800', 800") comprises a first section (800a, 800a', 800a") and a second section (800b, 800b', 800b") that is removably attachable to the first section (800a, 800a', 800a"), each one of the plurality of brackets (800, 800', 800") being attachable to the associated one of the plurality of differently sized tanks (400,400', 400") by attaching the first section (800a, 800a', 800a") to the second section (800b, 800b', 800b") to capture a portion of the associated one of the plurality of differently sized tanks (400, 400', 400") so that the tank valve (410, 410', 410") extends between the first section (800a, 800a', 800a") and the second section (800b, 800b', 800b"), and wherein, for each one of the plurality of brackets (800, 800', 800"), an assembly comprising the one of the plurality of brackets (800,800', 800' ') and the associated one of the plurality of differently sized tanks (400, 400', 400"), when attached to the bracket connector, positions the associated one of the plurality of differently sizedtanks (400, 400', 400") in a predetermined rearward position relative to the carrier system and at a predetermined height relative to the carrier system so that a distance (Dl, D2, D3) between a tank valve outlet of the tank valve (410, 410', 410") of the associated one of the plurality of differently sized tanks (400,400', 400") and the connector corresponds generally to a radius of a circular arc and varies by less than no more than 0.01270 meters (0.5 inches) for each one of the plurality of differently sized tanks (400,400', 400").