What are 1-2-3 blocks used for?

Step into any well stocked machine shop, and you’re sure to see a few 1-2-3 blocks lying around. These humble little tools may look like nothing more than over-sized, Lego-looking toys, but they’re essential for many things.


Named for the length of their three sides, 1-2-3 blocks are a trusted part of many tool kits. Whether you’re an aspiring machinist or a tradesperson who recently uncovered some of these steel blocks from the depths of their toolbox, this introduction to 1-2-3 blocks will give you everything you need to get started in putting these blocks to use.


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What is a 1-2-3 block?


You might be hard pressed to find another must-have, multi-use tool with such a simple design. The 1-2-3 block is nothing more than a piece of hardened steel, ground down to be precisely one inch by two inches by three inches. The sides are perfectly flat, the parallel faces are perfectly accurate, and the corners are perfectly square. The typical block weighs about a pound a piece, which makes them easy to carry around but heavy enough to use for weighing down paper in the shop.


Most blocks also come with a pattern of homes drilled and tapped into them, and some holes will have thread. The holes are often on all three sides of the blocks, and allow the blocks to be bolted to one another, which adds a slew of additional possibilities to the simple 1-2-3 block.


Because these blocks are so basic, they’re also affordable. You can find these tools — often sold in pairs — for sale at a wide range of prices and qualities. The higher prices generally indicate a higher attention to accuracy during production, but for many purposes a more affordable 1-2-3 block will do.


In addition to the 1-2-3 block, you’ll also see 2-4-6 blocks for sale. These, of course, provide similar possibilities but in different sizes. If you want the maximum potential from your blocks, consider getting a few sets of both sizes.

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When and how to use 1-2-3 blocks


There are so many potential uses for 1-2-3 blocks, that it would be almost impossible to cover them all here. Instead, we’ll go over some of the more common uses for machinists. Then, we’ll look at some of the more creative uses we’ve heard about in all kinds of shops.


Machine shop uses for 1-2-3 blocks


Most machinists use these blocks on a regular basis, and many of them have made their own. It’s a common practice for a machinist in training to be called upon to make a 1-2-3 block from scratch as one of their first assignments in trade school or apprenticeship. This early assignment is memorable, not just for the novelty but because the tool will be an intricate part of their machinist journey. Here’s how.


Tool touch off In a machine shop, it’s important to standardize tool offsets. This protects from any variation in job setup and is often done with by touching off a tool. Machinists can do this manually by using their 1-2-3 block and marking the offset as either one, two, or three inches depending on which side of the block they use.


Parallels With their precise surfaces and corners, 1-2-3 blocks are a great substitute for parallels.


Anchoring and elevating pieces When there’s a set of blocks on hand, machinists no longer have to worry about damaging their worktable. The blocks can be used to anchor the pieces to the table, and can elevate the piece either one, two, or three inches above the table’s surface.


Measurement A high-quality set of 1-2-3 blocks that are regularly calibrated is a perfect tool for quick and accurate measurements. They’re handy for checking that accuracy of a 90-degree angle.


Mill set up In CNC milling, it’s necessary to keep the work stable and secure while the machine mills the material. There are all kinds of complex fixturing that can serve this purpose, but in many cases a set of 1-2-3 blocks can meet a unique work holding need.


Other shop uses for these handy steel blocks


When you have a set of 1-2-3 blocks around, you’ll have no trouble finding uses for them. They really do come in handy in any shop, whether you’re using them for knife making or wood working.


Prop A small block with holes is helpful for the simplest reasons, like propping up an object. We’ve seen knife makers use a 1-2-3 block as a solid surface for removing a knife handle pin through one of the holes and are sure that they could serve as helpful props for tons of other items.


Vise When you need to hold an object stable, and you don’t have a vise on your workbench, you can turn to a set of 1-2-3 blocks. Simply tighten the object between the two blocks — but be careful not to over-tighten. This could cause the blocks to bend, and for this reason it’s best to use a cheaper set of blocks as a vise, rather than a set of precision blocks.


Measurement With their three precise lengths, these blocks serve as convenient tools for measurements. For instance, if you’re doing something like wood working and need to measure a slope, you can use two 1-2-3 blocks and a ruler to get a quick 1:12 slope.


How to choose the right 1-2-3 blocks for your needs


If you don’t have any 1-2-3 blocks lying around, don’t hesitate. Again, although you will find a range of quality and prices, these tools are relatively affordable and worth having around. Start with a cheap set and start discovering the possibilities.


Depending on your work, it can also be wise to buy two sets — one for regular use and one for precision. A set of precision 1-2-3 blocks should be used only for measuring surfaces and angles, never for something like clamping or anchoring. And, as with any precision tool, a 1-2-3 block should be calibrated regularly to maintain accuracy with every use.


Phil Wiseman

Phil Wiseman

Phil Wiseman is Chief Marketing Officer at Alliance Calibration. He earned a B.S. in Chemical Physics from Centre College. Phil is an ASQ Certified Quality Auditor and ASQ Certified Manager of Quality/Organizational Excellence.

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