I have 2 pairs of copper stub outs (1/2") and one 1/2" PEX pipe that I need to drill holes in porcelain tiles

I can't figure out what diamond drill bit size to order.

This chart tells me I need an 1" diamond drill bit but it seems too much

  • "That chart" is for schedule 40/80 pipe, (steel or PVC) which is very different from CTS (copper tubing size) and PEX tubing (outside diameter) for the same nominal inside diameter.
    – Ecnerwal
    Nov 22, 2021 at 0:57
  • PEX will need a larger hole than copper of the same size(thicker walls). You also don't want it to just fit. Measure PEX and give maybe 1/4 inch extra(or more) and you should be good, if your measurements for pipe placement are exact. If wanting extra wiggle room, 1 inch should work.
    – crip659
    Nov 22, 2021 at 1:01
  • 2
    They are exactly the same outside diameter. 0.625" Which is why a 1/2" sharkbite works on copper or pex.
    – Ecnerwal
    Nov 22, 2021 at 1:03

3 Answers 3


1/2" pex o.d is 0.625", a 3/4" would be fine. Don't know grade of copper but the wall should be thinner than pex, the 3/4" drill bit should be fine.

  • Any 1/2" copper pipe is 0.625" OD. The hole in the middle gets smaller for the thicker wall sizes (all slightly above 1/2" actual.) PEX hole size tends to be less than 1/2" actual (0.485" for the page I'm looking at to check on that right now).
    – Ecnerwal
    Nov 22, 2021 at 1:00
  • 1
    Find pipe/tubing sizes weird. No two 1/2 are the same.
    – crip659
    Nov 22, 2021 at 1:05
  • I figured if I said "all" 1/2" cu was the same somebody would find that one oddball type that didn't conform. Nov 22, 2021 at 1:06
  • Pipe sizes are about the size of the hole in the pipe (but only roughly.) So pipes with thicker walls are much bigger. Copper is by OD because copper fittings are soldered to the outside of the pipe, so it has to be consistent, even when the wall thickness changes. PEX evidently followed that model.
    – Ecnerwal
    Nov 22, 2021 at 1:10
  • So then is a 3/4in diamond bit ok ?
    – MiniMe
    Nov 22, 2021 at 2:08

It seems (I did some measurements, not sure why I did not do that before asking here :-( ) that even 1" is too tight and the holes must be very precisely positioned on the tile in order to be able to work with 3/4" 1" or even 1 3/8" seems to be more appropriate. I ordered this kit https://www.amazon.ca/dp/B07C8HQYZD


1-3/8 for pipe isolators, same hole for both 3/4 and 1/2.

  • A) OP noted he used a 1-3/8" bit almost 2 years ago. B) the rest of the answer isn't particularly clear.
    – FreeMan
    Jun 20, 2023 at 16:42

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