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Another tool I found useful during a recent installation of a solar-powered renewable energy system was the Irwin Unibit® #9 step drill that has what appears to be 14 total steps with two major steps sized (7/8″ and 1-1/8″) for 1/2″ and 3/4″ knockouts in electrical junction boxes and panels. We had more than one instance where an existing box had only 1/2″ KOs, and we needed to bring in some 3/4″ conduit. I suspect there’s an adapter for just this purpose, but the #9 step drill proved very handy and easily enlarged the holes in metal junction boxes. The Irwin 10239 Unibit® has a hex shank, a single-fluted cutting edge, and a SpeedPoint™ self-starting tip. They can be found online for $45 to $50.

Street Pricing [Google Products]
High Speed Steel Fractional Self Starting Unibit® [Manufacturer’s Site]
Irwin 10239 Unibit 9 Via Amazon [What’s This?]

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11 Responses to #9 Unibit Step Drill

  1. Shopmonger says:

    I love the uibit concepts for qick intsall jobs and things that don’t need to be 100% accurate. but $40 is a lot of dough….i use the 3 peicekit from HF adn have never had an issue.


  2. rob says:

    first off there would be little point to reduce a 3/4 conduit to half opening it can make it very hard to fish wires and such

    what you did is the correct answer to the problem

    the only thing I find with the irwin unibits is that they dull faster than a good lenox or greenlee and the are not sharpenable where as the 2 flute one you get from many places greenlee lenox and a few other places can be sharpened
    I regularly sharpen the tip of my 2

    I have this very unibit and 1/8 to 1/2 irwin bit as well with about 16 steps
    they work but for the money I can get 2 from the lenox or greenlee with the same stops

    but if this is your only option and it is easier to find in stores than the other two then by all means it makes a hole and does a good job

    stay away from aluminum it gums most step bits up and dulls them fast

  3. David Bryan says:

    There is a very simple misuse of fittings that’ll make 3/4″ EMT fit very nicely into a 1/2″ knockout. I’m not going to say what it is because you should never do it: if nothing else, the fitting isn’t listed for that use. Whatever size conduit you use, you have to end up with a hole that it fits. You sure can’t reduce the cross-sectional area by a trade size where the conductors enter the conduit.
    I’m not real crazy about using unibits for conduit entrances, but if you just want to enlarge a hole like this, they’re easier to center than knockout punches.

  4. Brau says:

    The replacement cost drives me away from these although I’ll admit they work very well while they are still sharp. Instead, I keep a full set of slug busters in my tool collection.

  5. Matt says:

    I’ll second the opinion that Irwin unibits suck, get a Greenlee, use it slowly with good pressure, lube it for stainless, don’t lend it to the miners or mechanics, and it will last a VERY long time.

    Irwin = GOOD for VISE GRIPS
    Irwin = BAD for STEP BITS

  6. Joe Sainz says:

    Has anyone used the Bosch ones? What are your likes / dislikes on them if so? Does something like hole quality or speed matter to you guys, or is just long life? The ones that I have used before (Irwin) did seem to dull quickly, so I guess I always wanted a longer life from them, and didn’t care about speed or a nice clean hole.

  7. fred says:

    My supplier provides us with the Klein brand – but the field crews often pick up Greenlees at the Big Box . I have not heard anyone say much about the differences (if any) noted.

  8. Matt says:

    The Greenlee ones cut fast if pushed, often spitting out colored (as in super hot) bits of metal, have to be careful when drilling up from underneigh a panel. The obvious downside is that they will dull faster, however I usually get over a year with mine as an electrician, used almost everyday. I usually get a new one when the tip dosen’t start a hole fast, however the rest of the bit still cuts great, so if you use a pilot bit they last very, very long.

    Sometimes the holes aren’t reall nice when you push the bit, but for electricians this isn’t usually a problem as a fitting is used in the hole anyway.

  9. kyle says:

    Matt do you think that iwin vise grips are still good now that the manufacturing plant was moved to china?

  10. Matt says:

    I haven’t tried any new ones… but I don’t like the crap plastic grips they put on, as if they have to add that stuff to compete…

    I’m also confused why you would want to turn the adjustment screw with an allen wrench (like on the newer vise grips)…anyone have input on that?

  11. Joseph Stevens says:


    As I understand it, the reason for the hex key on the screw is to allow for an easy release. If you have ever locked a Vise Grip on real tight and tried to pull them apart, they have that explosive action. If you loosen the screw with the allen key, they come off really easily. I would assume the same is true for applying more pressure for clamping if you are unable to lock them down as tight as you would like them to be. The new ones I have are just fine and I do not notice any perforamce difference.

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