During a scientific research, directed to understand the structural role of some particular masonry elements, noticeable in covering structures like vault and dome, we searched the technical rules and function of these elements. We verified that in literature there is no specific documentation about these elements and its mechanic purposes. The study was directed to recognize the most representatives architectures in different ages, and to identify the construction technique’s evolution process of this particular arc-double or thickening of arc that we arrived to identify as a necessary building component to give balance in particular structural configuration. This process put down roots from the roman ancient age, until baroque age, where the most original applications of this regulation were placed. From Pantheon to the limit case of St. Filippo Neri chapel, the covers’ structures springer angle studied was analyzed together with its relation to plan, sections and elevation of all buildings. Therefore, if these elements are well-performed, they follow precise constructive patterns that this article would like to identify and show.