I think both are probably correct in regard to specimens they were describing. The Pattern 1838 waist belt was 1 1/2 inches wide and 38 1/2 inches long for Infantry and Riflemen. In 1844 regulations were changed for Riflemen to a 2 inch wide belt. The Infantry belt remained 1 1/2 inches wide throughout the Mexican War. The belt plate is not described correctly in the 1839 regulations. The plate had wire hooks. In any case these wire hooks were replaced by hooks of sheet brass after 1844. Shoulder belts were no longer regulation during the Mexican War, if old equipment may have been issued is another matter.
I sell an excellent little paperback that may be of some help. Historical Arms Series No.20 ACCOUTREMENTS OF THE UNITED STATES INFANTRY, RIFLEMEN, AND DRAGOONS 1834-1839 by R. T. Huntington. $8.95 plus postage.
Hope this helps,
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