I understand that my brushless cordless 20V (Dewalt) drill—because it has a hammer option— has what it takes to drill a 16 mm hole into concrete.

I also understand (from the same answer just linked) that I shouldn't just drill directly with 5/8". I have to first drill with maybe 4 mm, 8 mm, and 12 mm, before using the final bit.

I still have a few brief questions regarding drilling into concrete.

  1. The drill bits sold in my area are imperial, not metric. Will a 16 mm anchor bolt give me a hard time when I hammer it into a 15.9 mm hole?

  2. The bottom two feet of my garage wall (outside wall) look like concrete. I'm setting up a bike lock in it. After I install the lock, I'll tug with all I've got to confirm it's firm, but how do I confirm before starting that it's actually concrete?

  3. Since the other side of the wall is outside the house and since this is away from light switches and any water pipes, I'm expecting there are no electricity and no water pipes. What is the likelihood I'll drill into water or electricity when it's a lower outside wall in a garage? Water pipes are never burried in a concrete wall; are they?

  • water pipes and electric conduits might penetrate the concrete but they are newer buried in it.
    – Traveler
    Sep 12, 2022 at 23:39
  • as for drill size, start with pilot hole about 1/3 of the final size (16/3 = 6mm or 1/4 inch drill, then use 2/3 of the final size, then final size
    – Traveler
    Sep 12, 2022 at 23:42
  • 1
    water pipes can come up frm the ground through a concrete wall, it would be quite normal on a slab-built house.
    – Tiger Guy
    Sep 13, 2022 at 5:38
  • "Buried" as in "encased in" - sure, you'll get water, electrical, and nearly everything else running in your walls if they're made of concrete and you don't see them on the surface. They have to be somewhere, so if they're not visibly attached on the surface, they'll be within it.
    – FreeMan
    Sep 13, 2022 at 15:17

1 Answer 1


I do not really understand your use of Imperial and Metric. Can you not get the correct drill bit and the correct anchor bolt ? Anyway, you probably will be able to get your 16mm anchor bolt into the 15.9mm hole as the big masonry bits do tend to move around a bit as you are drilling.

If you want to do the step up size drill bits I guess that is OK. You could also rent the correct size hammer drill and a bit from your local rental store. This way you can drill in one shot the correct size hole and maybe even save some $ by not having to buy a bunch of different size drill bits. Drilling a 5/8" hole without having to pre-drill smaller sizes first is done every day.

As far as pipes and conduits in the wall I wholly disagree with some of the comments above. There are definitely pipes and conduits and gas lines in concrete stem walls. Whether there are pipes where you are planning to drill- no one knows. The only sure way to know is to remove some of the wall covering (drywall I would guess) above the stem wall and look. Chances are there is not anything there right where you want to drill but, if there is something there at the least it will cost you time and money to repair (not an easy repair) and you could greatly harm or kill yourself and others. I am not meaning to rain on your parade but it needs to be said.

  • Not everyone can or wants to rent tools or purchase new toys, er, tools. For some it's a "get the job done with what I've got" process. If an impact driver is all that's available, that's what you work with. 100% agree with checking the wall above the concrete (or possibly in the attic above or crawlspace below) for pipes & wiring in the stud bay above where the drilling will take place. Tearing out & replacing drywall to check will be MUCH less work & expense than repairing plumbing or electrical in concrete.
    – FreeMan
    Sep 13, 2022 at 15:21

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