Abstract: The four metal panel portions of an air conditioning unit roof curb have spaced sets of inwardly projecting lanced portions positioned adjacent their ends and defining tab-receiving slots. With the panel portions in a rectangular assembly orientation, specially designed drive cleats are used to lock the contiguous ends of the panel portions together at the corners of the curb. Each cleat has spaced pairs of tabs which, when the cleat is downwardly driven into place on a corner section of the curb, sequentially enter vertically successive pairs of slots in the contiguous panel end portions at the corner. In this manner, only one tab pair and one slot pair need to be aligned with one another before the cleat is driven into place to lock the two contiguous panel end portions to one another, the initial tab pair/slot pair alignment serving to automatically align the successive tab and slot pairs as the cleat is driven home.