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I was looking forward to buying a drill for my crafts when I found this under the drill's photo:

specifications

I was wondering what do the metrics under the brick, wood and steel refer to? At first, I thought it was the maximum depth I can drill in these materials, but then I thought that this depended on the drill size and that it couldn't differ among different materials, so what are those numbers really for?

  • Can you link us to the drill page where you found this as well? – Matt Sep 1 '16 at 12:00
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The numbers shown represent the maximum recommended drill bit diameter for the material shown.

Max diameter "masonry" drill bit is 32 millimetre

Max diameter "wood" drill bit is 42 millimetre

Max diameter "steel" drill bit is 13 millimetre

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Thats the maximum bit diameter. There are a couple of limits that are relevant: the outside of a large drill bit moves fast, so you may have to slow the drill down, but then it becomes less powerful and could stall. An optimised drill bit is assumed (e.g. using an HSS bit in wood is fine for many tasks, but at the large end it won't work). In practice you can often go a little bigger than they say with flat wood bits:

Flat wood bits (via wikimedia commons)

or hole saws if you're gentle.

For many applications it's possible to have a drill with a shank that's smaller than the cutting end, hence the chuck size is less of a limitation. For example step drills are used for drilling sheet material:

Step drill This one has a shank of about 10mm and a maximum hole size of 26mm, mainly for metals.

Reduced shank drills (or blacksmith drills) are used for deeper holes, again mainly in metals. These are a 16mm and a 25mm, with 13mm shanks:blacksmith drills

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  • The pictured bits are more than a little misleading since spade bits are intended for wood (or other relatively soft materials) and will quickly dull and wear down in brick or steel regardless of the diameter. – Ast Pace Sep 1 '16 at 15:21
  • @AstPace when I put the picture in I was trying to find examples of blacksmith drills as well to illustrate the next point -- but couldn't find any with the right permissions. The image is captioned (and has alt text) "flat wood bits" so it shouldn't mislead anyone – Chris H Sep 1 '16 at 15:25
  • On other Stacks (e.g. woodworking) a simple credit or link to the source is considered sufficient to display an image. So you can certainly slip the image that you have linked into your answer. – Ast Pace Sep 1 '16 at 15:58
  • @AstPace, I'd rather take a picture myself, but might not have the time. I don't think there's currently a consensus across the network and I come down on the side of only embedding libre resources. – Chris H Sep 1 '16 at 16:53
  • I don't know enough about the bits, but you could always make a list of links to images or sites that show the exact bits you want, if you need more and don't want to directly embed. – user24 Sep 1 '16 at 17:18

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