Abstract: This disclosure relates to a fastener driving device which produces a slot around a shank of the fastener as it is being driven. It is useful in a situation where a sheet material which is subject to expansion and contraction is to be fastened to a base and wherein movement resulting from expansion and contraction must be permitted to avoid buckling. The invention resides specifically in the guide body and driver element of the tool in that the driver element is T-shaped in cross section with the central portion of the T constituting the driver proper and the portions extending laterally from the central portion terminating below the bottom of the driver proper and having a recess extending from the bottom of the driver proper through the length of said punch into which the shank of a fastener may be pushed. In this way as the fastener is driven into the base through the sheet material, a slot is formed extending to both sides of the shank of the fastener.