Disston Screwdiggers fulfil the same function as Screwsinks but the countersinking part can be slid up & down the drill part of the tool. This means, for example, that a No.8 Screwdigger can be adjusted to predrill for different lengths of No. 8 Screw. This set contains 1 each No. 6, 8, 10 & 12 screwdiggers.