Introduction to 1-2-3 Blocks

March 19, 2021 9:57 am

What is a 1-2-3 block? You probably remember these gems as one of your first machining projects back when you were in school or during your apprenticeship. 1-2-3 blocks are blocks of hardened and ground steel. They are called 1-2-3 blocks because their sides are 1,2 and 3 inches long, respectively. There are also larger versions of 1-2-3 blocks that are called 2-4-6 blocks.

There isn’t one right way to use 1-2-3 blocks, in fact, the amount of uses is exponential and can look different from one shop to the next (this one really caught our attention). Using precision blocks or 1-2-3 blocks requires creativity because they can be used in many ways—some that are up to you to think up!

Common Ways to Use 1-2-3 Blocks

1-2-3 blocks come in handy for inspection and measurement tasks. For example, they can be held against an edge to create a protruding face in which to use the given measuring tool.

They are commonly used as parallels. They can be placed under the part so that through holes can be drilled through the part without damaging the table. Precision 1-2-3 blocks are also useful for anchoring pieces to your worktable so that they are in an elevated position.

In milling operations, these blocks are commonly used as a square reference or a mounting point. 1-2-3 blocks are handy for accurately representing lengths, making them similar to gage blocks.

Additional uses for 1-2-3 blocks include:

  • Precise grinding, and layout work
  • Check tool length offsets
  • Indexing jobs
  • Creating and recreating setups

How 1-2-3 Blocks Work

Although not always the case, 1-2-3 blocks typically feature cross-drilled holes. These holes are there for a couple different reasons. For starters, they enable you to connect the blocks to one another and/or to the worktable with bolts, allowing you to create different configurations, making application possibilities endless.

The holes also make the block much lighter, making it easier to handle. These holes can be threaded, though 1-2-3 blocks typically have a combination of threaded holes and non-threaded holes.

Depending on where your 1-2-3 blocks will be used in the shop, it’s important to have an air tool to clean out the holes so that coolant, dust, and chips don’t build up in the hole or interfere with your work.

Make Your Own 1-2-3 Blocks

Machining your own 1-2-3 blocks requires a high level of precision and accuracy because of their versatility in a machine shop. They must be precisely squared and parallel. Below is a video that will walk you through the process if you’re interested in making some yourself.

1-2-3 Block Models

Beware: it is common to purchase a 1-2-3 block and the holes end up being a bit too small for your needs. This can be solved by enlarging them yourself, but keep this in mind when selecting a 1-2-3 block and save yourself from any surprises.

WEN 10423 Steel-Hardened Precision 1-2-3 Blocks, Two Pack

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Calibrate equipment, space workpieces, or collect exact measurements with this set of precision 1-2-3 blocks. Each block measures 3x2x1 inches, perfect for machinists. The WEN blocks feature five threaded M10-1.5 holes and 18 unthreaded holes.

Anytime Tools 1-2-3 Blocks

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These Anytime Tools Blocks are made of precision ground steel and are case hardened on all six sides. The squareness on all sides is within 0.0001” and the surface finish is from 6 to 16 microinches. There are 23 total through holes (5 tapped 3/8″-16 TPI and 18 plain).

TEXALAN 1-2-3 Blocks Hardened Steel 1 Hole

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The flatness and parallelism of the TEXALAN 1-2-3 blocks are within .0001″ and the squareness on all sides is 0.0003″ per inch. These are great for setup, layout, and inspection jobs.

Shars 1-2-3 Precision Matched .0002″ Pair Blocks

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The Shars 1-2-3 blocks are ideal for precision, grinding and layout jobs. The blocks are precision ground and hardened on all sides. The hardness is 56 to 60 RC. If this exact set isn’t right for your needs, there are other models with different amounts of holes.

Taytools 469744 1-2-3 Blocks No Holes Matched Pair

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As mentioned earlier in the article, not all 1-2-3 blocks have holes, like this Taytools model. The block was produced from professional quality precision ground steel and case hardened to RC 55-62 on all six sides. The squareness on all sides is within 0.0002″.

You probably noticed that not all 1-2-3 blocks feature the same number of holes and you might wonder if it’s there’s a rule to choose the right number. Don Bailey from Suburban Tool Inc. shared some tips on how to select the right style in the video below. Check it out!


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  • lathechuck says:

    I see tight tolerances on squareness (which implies parallelism, according to Euclid), but the overall dimensions are described just as 1x2x3 inches (without tolerances). I see some sold as a matched set, which implies that the relative tolerances within the set must be tighter than the overall tolerances. So, what are typical tolerances on the overall dimensions?

  • chewietwo says:

    I got in the trades 37 years ago, when we made all or own tooling like 1x2x3. At this time there are 10 1x2x3 blocks in my toolbox! lol Some with holes, some solid but all ground the same. When running the big jig bores and vertical and horizontal milling machines that i have i needed more than 2 blocks ground the same. I made some with out holes for use on the grinders and some with holes so i can bolt them ether to one another or other tools (sine plate, cube or others) Both kinds have been useful which is why i cary both in my box. I think with cnc’s taking over most shops and machinist will buy what they think they will need. which is a shame to lose out on a great learning tool!

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