The part that interests me is marked in the picture. I have no tool that utilizes that part of a bit and I cannot find any clues on the net... In fact, all of my bit holders have better grip on bits without that indentation. So what's that indentation for?

Sample bit


4 Answers 4


Impact (or hammer depending on your region) drivers have a locking mechanism which holds the bit in place:

Ridgid 18v impact drill

Usually the drill bit will just snap right in. To remove it you need to pull the collar forward and the bit will pop out.

Typically you would buy impact-grade bits such this one which are designed to twist at a specially designed weak point so that the phillips end does not fail and break.

Milwaukee PH2 bit

A hammer drill is typically used to drill holes in concrete as it exerts a hammering action to break up the material which it drills into.

You can get a dedicated hammer drill or lots of standard drills have a hammer option (not as effective as a dedicated hammer drill but good enough for small-ish holes).

An impact driver does not exert a hammering action. This can be confusing depending on the terminology in your region.

Not to be confused with an impact wrench which natively accepts sockets for automotive work.

Milwaukee also produces a 6 inch locking bit extension which will hold the bit in place using the same principle as the impact driver's collar:

Milwaukee 6 inch locking bit holder extension

So you could attach this to a regular drill and always have the convenience of a locking collar for quick bit changes.

  • @Nebril They are super useful. I amended my answer with a locking bit extension that I really love using. Paired with drills bits like these it is an absolute pleasure: homedepot.com/p/…
    – MonkeyZeus
    Dec 23, 2020 at 16:08
  • 5
    While this answer isnt incorrect, I think the material about hammer and impact drivers, the majority of the answer confuses the issue; the system is part of a quick connect/release used by just about all types of drill/driver tools. Dec 23, 2020 at 23:54
  • 1
    I carry a 6" and a 12" extension which often get put together and then a finder driver to get like 2' away. Kinda wobbly but it works. It's super fun when you have put a right angle drive onto all of that....
    – Mazura
    Dec 24, 2020 at 1:33
  • This is correct. I have an on-bike tool kit with these bits, and a chain breaker that lacks the indent. So there's nothing holding the chain tool to the handle, and it frequently separates when changing grip. So yes missing one makes you appreciate them more.
    – Criggie
    Dec 24, 2020 at 3:06

It sounds like the bit holders you have are magnetic. Magnetic bit holders are really only suitable for light duty.

Most professional level bit holders employ a quick release system, whereby you'd pull (or occasionally push) a retaining ring. This ring releases a holding mechanism which slots into the groove on the bit. This prevents the bit or drill bit from falling out during use, potentially causing injury.

  • I dont quite agree. As an electrician I mostly use magnetic bit holders, and so does many of my colleagues. Also for heavy duty / high torque use. Occasionally the tip falls out of the holder, but that is often outweighed by how easy and quicly you can change the bit. Specially if you are doing a job where you need to swap bits a lot. Dec 29, 2020 at 21:12
  • @handyman, my bit holder are magnetic. But some are also locking. They don't work well with bits in question but they lock pretty well on regular short bits.
    – Nebril
    Dec 30, 2020 at 19:57
  • @Mads Skjern, in my experience the locking holder are easier than simple magnetic ones. They actually eject the bit a little so it's easier to work with sweaty hands or greasy gloves.
    – Nebril
    Dec 30, 2020 at 20:00

I am late to the party I am afraid. Anyway. Those indentation or groove is the place for the balls to fall to, in the quick release collet type chuck usually found in impact drivers. These type of Chucks have a arrangement of small steel balls (the same kind found on bike bearings) on the inside of the slot hole around the bit that you insert. They are usually pushed radially in, by the collet due to its spring pressure. When you pull the collet against the spring pressure to insert or remove the bit, it moves away from the balls allowing the balls to move radially out and make way for the bit to go in our out freely. Once the bit is in place in the slot, the balls will be directly over the groove on the bit so that when the collet is released, the spring will push the collet over the balls and the balls will move in and sit on the bit's groove, locking the bit in place.

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    – Community Bot
    Jul 9, 2022 at 20:55

The indent is to allow the jaws of your drill chuck to firmly tighten onto whatever driver you are using.

A dills chuck usually has 3 jaws that are able to raise (tighten) or lower (open). If you look at the inside section (the one that contacts the driver) you'll see they have an oval like profile. This gives the jaws more grip onto the bit and locks it into place.

Also, I've found that 1/4 inch shape at the driver/bit bottom fits perfectly into any bit extension. So if you need to drill a deeper hole with a spade bit it will hold nicely in an extension bit holder.

  • 6
    3-jaw chicks don't need the indent to grab bits, many bits have constant diameter shanks and 3 jaw chucks hold them just fine. As the other answer said, it's effectively part of a quick connect/release system. Dec 23, 2020 at 23:48
  • the flats are for the jaws to grab, but I think this question is about the narrow part.
    – Jasen
    Dec 24, 2020 at 12:52
  • 2
    @Jasen all my drills have 3-jaw chucks and grab hold of round drill bits just fine. The flats actually make it more difficult to put one of these bits into a regular 3-jaw chuck because you have to line up a flat with a jaw just right or the bit will pop loose and come out. The flats are designed to fit into the hex-shaped holes in impact drivers that do not have a 3-jaw chuck.
    – FreeMan
    Dec 24, 2020 at 14:22

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