Modularity has been defined at the product and system level, however little effort has gone into defining and quantifying modularity at the component level. We consider complex products as a network of components that share technical interfaces (or connections) in order to function as a whole and we define component modularity based on the lack of connectivity among them. Building upon previous work in graph theory and social network analysis, we define three measures of component modularity based on the notion of centrality. Our measures consider how components share direct interfaces with adjacent components, how design interfaces may propagate to non-adjacent components in the product, and how components may act as bridges among other components through their interfaces. We calculate and interpret all three measures of component modularity by studying the product architecture of a large commercial aircraft engine. We illustrate the use of these measures to test the impact of modularity on component redesign. Our results show that the relationship between component modularity and component redesign depends on the type of interfaces connecting product components. We also discuss directions for future work.