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When cutting precision joinery by hand, sometimes a joint that’s off by a fraction of a degree is the difference between it seating or splitting apart. When diagnosing joinery problems of students, I use a vintage diemakers square (I wrote about this in 2013 here). It allows me to sneak into places no normal square can go and is more accurate than my eyeball.

Diemakers squares can be expensive, so I was thrilled to see that Chris Kuehn of Sterling Tool Works has produced a Dovetailing Ruler that can fit into a standard 6” combination square, converting it into a superb diagnosis tool.


The $25 ruler is the exact same thickness as the standard blade for a 6” square, .075”. Its major width, .329”, allows the blade to sneak under the square’s clamping screw to lock it down. The small leg of the ruler is .091” wide, allowing you to get into the smallest joints.

The Dovetailing Ruler is a fantastic idea and is much less expensive than a diemakers square. Even though I don’t need it for the dovetails I personally cut, I will definitely be using it for double-checking some hand-cut finger joints in my next project where dead-on perfect is the only way to go. Also, these little blades are great for checking the depths of small holes and a hundred other uses at the bench.

If you’re a machinist, you can make one for yourself. But the rest of us without milling machines should click here and order one. Highly recommended.

— Christopher Schwarz

P.S. The Dovetailing Ruler is .010” too thick to work in a 4” combination square, but making the Dovetailing Ruler thinner would not have been a good idea in my opinion.

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Showing 7 comments
  • Andrew Robb

    I will say from the out set I am biased as I know Chris and am Australian but…
    His double square is an amazing piece of tool making and kicking back, drinking coffee and talking about machining and what square means while Chris hand cuts dovetails is an experience. He can’t help himself just got to keep those hands busy.

  • Alex

    Perfect timing, my double square just suffered an unfortunate accident so I ordered the serling Double Square which comes with a dovetail ruler.

  • Derrick

    Any idea if this will fit into a Starrett 4in combo square, or just the 6in?

  • Derek Cohen

    Yes, and another vote for the Vesper double square. More expensive, but a lifetime tool, and likely easier to use. Get the standard and the mini blade, as Megan indicates.

    Regards from Perth


  • toddmarstall

    For once I am a step ahead of Chris. Picked one up at Handworks before he could write about it and create a backlog. 🙂

  • Paul Moldo

    Does Chris Vesper’s double square do the same job?

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