How to Tap a Counterclockwise Thread


Tapping a counter-clockwise or left-handed thread after you have drilled a hole is nearly identical to the process of tapping a standard threaded hole. The only difference is the direction that you turn the tap handle. With a standard tap, you turn the tee-handle clockwise to start the thread into the hole. It will seem awkward at first; turn the handle the other direction and harder to keep the tap running straight in the drilled hole.

Things You'll Need

  • Left-handed tap
  • Tap tee-handle
  • Cutting and tapping fluid
  • Rag
  • Open the tap tee-handle wide enough to receive the square end of the left-handed thread.

  • Insert the squared edge of the left-handed tap into the tap tee-handle and twist the clamping handle of the tee-handle clockwise to lock the tap into the tee-handle.

  • Run cutting and tapping fluid down the drilled hole and coat the left-handed tap with the cutting and tapping fluid.

  • Place the tip in the drilled hole and hold the tap tee-handle parallel to the surface of the metal you are tapping.

  • Turn the tap tee-handle counter-clockwise with both hands steadying the tee-handle.

  • Continue turning the tap tee-handle counter-clockwise while you carefully keep the tap perfectly straight. If you notice that the tap requires more force to turn, reverse the direction you are turning the tap tee-handle to back up the tap. This removes metal shavings from the cutting threads of the left-handed tap.

  • Run the tap all the way down to the surface of the metal. Do not force the left-handed tap beyond the threads, as this will break the brittle carbide tap.

  • Turn the tap tee-handle clockwise to reverse the tap from the now threaded hole.

  • Clean the area around the threaded hole with a rag.

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