The BLACKHAWK! CQC Carbon Fiber Double Row Magazine Case-9mm/.40cal Carbon Fiber Finish (Black) has a built-in tension spring to hold your magazine in place until you need it and to allow the use of a variety of magazines in each pouch. Can be placed side by side on our Dual Rail Accessory Platform, for those wanting a double magazine pouch, on the same carrier. Or, they can be placed beside one of our light carriers, for a combo light/mag carrier.