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I'm new to drilling but I've read up as much as I can.

I need to drill some 8mm holes in brick (not the mortar) for 8mm rawlplugs.

I'll be using a 550W Bosch corded hammer drill and I have a set of masonry bits at 3mm, 4mm, 5mm, 6mm and 8mm (they are hex shank, I chose that because in several reviews of the drill people were complaining about it losing grip - it's a keyless chuck with 3 jaws).

I have a center punch to mark the initial drilling point.

Suggestions for sensible pilot hole size? (The rawlplugs are 8x32 so I was planning to go around ~40mm deep for the final hole).

Also is a good idea at the very beginning not to use hammer mode, to get the hole position correct?

I'm guessing in some situations people might drill more than one pilot hole, but maybe not for a hole this small? (Thanks)

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    8mm is ~3/8". I don't think you'd really need a pilot hole for something that small. I certainly wouldn't bother. You may want to wait to see if someone has a good reason to do so.
    – FreeMan
    Mar 10, 2022 at 12:29
  • @FreeMan 8mm is about 5/16" - if you drill a 3/8" which is apporox 10mm then that rawlplug will be like a pruck in a bucket…
    – Solar Mike
    Mar 10, 2022 at 12:48
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    Thanks, @SolarMike, that was a very rough in-my-head calculation, and I was wavering between 5/16" & 3/8". :) Either way, IMHO, that's not big enough to need a pilot hole.
    – FreeMan
    Mar 10, 2022 at 13:12
  • sorry, here in the UK I've only ever seen drill bits measured in mm so I didn't think to convert… Mar 10, 2022 at 13:20
  • Converting should not matter if everything is metric or standard. In Canada it matters since we would drill a 10mm hole for a 3/8 inch dia bolt.
    – crip659
    Mar 10, 2022 at 13:35

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Unless you need extreme precision for your holes (and I'm not sure you'd get it even with a pilot hole), just drill your holes with the 8mm bit.

Just a few weeks ago, I drilled a couple of 7/8" holes (roughly 22mm) through brick (not the mortar) with a hammer drill and no pilot holes and had absolutely no issue.

The only issue I did run into was that one of the holes went through 3 layers of brick when I thought it was only 2, so I scuffed up the chuck getting through the last few mm of brick because my bit was just barely long enough.

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  • Thanks for this. Lessons learnt: second hole took ages because it turned out I was drilling at a downward angle; also I made the mistake of attempting to use an electric screwdriver to fasten the screws, not enough torque so damaged the posidrive heads (slightly), much better when I used ratchet. Ear defenders worked well, not nearly as noisy as I was expecting. Cup of water to cool/clean drill bit was useful. The bit still came loose a few times, even with hex shank… Mar 10, 2022 at 18:02
  • Not sure bit cooling was necessary, @WilliamTurrell, I didn't bother with my 7/8" holes, but I'm sure it didn't hurt. TBH, I've always had trouble getting hex shank bits to line up nicely in a 3-jaw chuck. You have to ensure that the flats of the hex meet up with the curve of the jaw. To me, it's just more bother than it's worth. I use hex-shank driver bits in my impact drivers all the time, but I stick to round drill bits. YMMV.
    – FreeMan
    Mar 10, 2022 at 18:42

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