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I have a 3/8 hand-held drill and that's pretty much all I need for my projects. But now I have a project where I have to insert large dowels, and they will need a 7/16" hole. I don't have that size bit, but before I rush out and buy one only to find that it won't fit my 3/8" drill, I want to know if there are adaptors or other tricks I can use to make it fit.

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    If this is for drilling in wood, there are spade or fostner bits that will make large holes with a small shaft that will fit in a 3/8 drill. There are also bits with the shaft stepped down to fit 3/8 drills if you want a regular bit. Just buy bits for 3/8 drills.
    – crip659
    May 13 at 21:14
  • Just bought a 28mm bit with 1/4" hex shank for fitting dowels…
    – Solar Mike
    May 13 at 22:43

3 Answers 3

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You can find reduced shank drill bits that have 3/8" size shanks for drills like yours that go up to sizes up to at least 1/2" and more. I have several drill sets that include these.

You can find these almost everywhere. Check online with this search phrase "reduced shank drill bits".

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  • Yup, I have a set that looks very much like your second picture--a whole range of sizes. I think the set was only like 2x or 3x the price of an individual bit. Ordinary item at the local big box hardware store. May 15 at 3:11
  • This is exactly what I ended up doing and it worked well.
    – user766353
    Jun 4 at 20:30
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There are bits with shanks ground down to 1/4", 3/8", 1/2" dimeters to fit chucks. They may need to be special ordered and may be expensive. I have several but I inherited a bunch of bits so I don't know what they cost. I have also ground 3 flats on shanks when they were a little too large for the chuck ( assuming you have a 3 nib(?) chuck).

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    Doubt that 3/8 sized shanks need special order or expensive. Even most cheap bit kits for 3/8 drills will have the larger bits sized to fit. 3/8 drills are quite common.
    – crip659
    May 13 at 22:28
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Since this is on "home improvement" and you are mentioning dowels and a handheld drill, I assume you are working in wood.

Another answer has suggested searching "reduced shank drill", when I tried this I got mostly twist drills. AIUI twist drills are primerally intended for drilling metal and while they can be used on wood, another type of bit is likely to be more appropriate for drilling large holes in wood.

My understanding is there are three main options for drilling large holes in wood. In my experience all of them will come with shanks small enough to fit in a standard drill, but I'm in the UK where a standard drill can take a 10mm shank, I don't know what things are like in the USA.

  1. Spade bits, these are the cheap and rough option for moderate size holes.
  2. Forstner bits, these are the cleaner and more expensive option for moderate size holes.
  3. Holesaws, these are the best option for really big holes because they do less cutting work then other tools. However removing the plug of waste from the holesaw can be annoying, depth of cut is limited, and they can't drill a blind hole (though they could be used to define the edge of a blind hole before removing the waste with other tools).
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  • I use hole saws when drilling all the way through, which means the plug comes right out. Wouldn't want to try for creating a hole for a dowel, that would be extra work and maybe leave me with a not-so-perfect hole. I considered using a spade bit but didn't really like the extra depth created by the center point.
    – user766353
    Jun 4 at 20:32

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