I want to install a sink soap dispenser but the existing hole in my sink is too small. From what I've found the universal diameter of the threaded piece that inserts into the hols is 1 inch. My hols is closer to 3/4 inch. So, how can I increase the size of an existing metal hole in kitchen sink? My research so far has led me to using a piece of clamped 2x4 as a guide for a drill bit but I cannot clamp the wood to the sink. Any ideas?

2 Answers 2


You should be able to use a knockout punch.

knockout punch

These are inserted through a pre existing smaller hole, and can cut sheet metal including stainless steel. They come in a range of sizes.

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  • You'll need to remove 1/8" all around the perimeter. It will be easiest with a Dremel (or similar tool) and conical composite grinding bit. Not that it will be easy to do....stainless steel sheet is relatively difficult to grind. Use your bit at high speed and hold on tight as it will want to jump once it grabs the metal. Grind gently and don't force the bit into the edge. Good luck! Commented Jan 20, 2017 at 21:58
  • @KnobScratcher Sounds like an answer.
    – bib
    Commented Jan 20, 2017 at 22:41

I did exactly this recently using a standard drill, small bits, and a cutoff wheel in a rotary tool (Dremel). I marked the circle and drilled a series of small holes using high-speed steel bits of around 1/8" in size. I then cut between the holes with the cutoff wheel. It leaves a somewhat jagged hole, but it was easy and free and isn't visible once the dispenser is installed anyway.

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