While this distribution was initiated to support Zen Cart 1.5.3 and Zen Cart 1.5.4, a version that combines all of the necessary code to support operation in Zen Cart versions 1.5.1, 1.5.3, and 1.5.4 (and potentially 1.5.5 and above) is available from https://github.com/mc12345678/Stock_By_Attributes_Combined. Improvements made there have not been back populated to this distribution and there is no plan at this time (4/2016) to do that.
Stock by Attribute (SBA) for Zen Cart 1.5.3 and Zen Cart 1.5.4
This SBA Modification will only work with Zen Cart 1.5.3 and Zen Cart 1.5.4. This is due to the new functionality and code changes that have been added to support the newer version of Zen Cart.