Abstract: A slotted inverse tap, compressible for insertion past damaged entry threads in blind holes. (FIG. 1 thru FIG. 5) The tool can be made to smaller sizes than that of prior art. An elongate slot (23) proceeds through a first threaded end (21), then well into a reduced diameter cylindrical body (25). After insertion to the hole bottom, a tabbed shim (28) is inserted to the slot from its side, then pressed down until stopped. The shim (28) enforces mating engagement with undamaged internal threads. A second end of hex and/or squared or other configuration facilitates use of a tap wrench or other tool for rotational extraction. Damaged threads are reformed/re-cut upon rotational withdrawal.

Abstract: An adjustably expandable fluted tap to reform damaged threads defined in a blind hole, such as a spark plug hole. The tool provides an elongate body with a first end defining an expandable fluted tap having a relaxed diameter smaller than but matingly similar to the threads to be repaired, and a second end defining a butterfly handle. The body defines a medial channel carrying an arbor with a first end having a tapered forcing cone for expanding the fluted tap, and a second end threadedly engaged in a round knurled nut carried externally of the second end of the body. The tap is inserted in a hole beyond the damaged threads, the knurled nut tightened to retract the forcing cone to expand the fluted tap into mating engagement with the undamaged threads and the tool is then screwed out of the hole by revolving the butterfly handle to reform the damaged threads as it is withdrawn therepast.