The original pouches for the 15-round carbine magazines were designed to be worn on the pistol belt in place of the double pouch for the .45 pistol magazines. The carbine was designed to replace the pistol for troops normally assigned one. As a result the pouch had a snap fastener to allow it to be attached to the corresponding stud on the pistol belt. The snap fastener was attached to a sleeve. The pistol belt could be slid through this sleeve so as to mount more than one on an issue pistol belt.
Alternatively, it was found that the sleeve arrangement allowed the magazine pouch to be slid over the end of a carbine and would fit nicely on the stock. The stock put enough pressure on the sleeve to keep the pouch in place and a total of 45 round of .30 carbine could be carried on the weapon itself: 15 in the loaded magazine (in rifle) and two loaded 15-round magazines on the stock.
Later on, the design of the magazine pouch for the 15-round carbine magazines was changed to two parallel cloth straps. This pouch would slide onto the pistol belt, but there was no fastener to attach it to the stud on the belt, nor would it fit onto the carbine as the early pouch did.