Diameter-mismatch approach:
The defining feature of topworking an old fruit tree is that the stock, the tree's existing branches, is far thicker than the new scion wood being introduced. Whip and tongue, and splice grafting both require the scion and stock to be of near-equal, pencil-like diameter, which makes them unsuitable once a tree's branches have thickened with age. Cleft grafting solves this size mismatch directly: the thick branch is split down the middle, and one or two slender scions are wedged into the cleft so that their cambium layers align with the cambium at the edges of the much larger stock. Because this technique is built specifically to accommodate a large stock and small scion, it is the standard method for reworking established, older fruit trees.