The tula adze is a distinctive composite tool that was used in the Australian arid zone during the late Holocene. In this paper we use design theory to investigate why this particular tool form was so pervasive across time and space. Design theory provides a rational means for classifying tool designs and for determining why particular tool design classes were employed over others. We draw upon ethnographic and archaeological evidence to characterize the design of the tula adze and conclude that it is consistently the product of a “reliable” design strategy. We further determine that the high cost of a reliable design was chosen because the tula adze was employed in situations where failure could not be tolerated. Specifically, we argue that an important role of the tula adze was to manufacture wooden goods for not only personal use but more significantly for trade. The quantity and quality of these goods had an extremely strong bearing on the economic sustainability of arid zone Aboriginal groups.