123 Blocks and the Hardware Kit That Fixes Their Biggest Flaw

Introduction

123 blocks have been around for well over a hundred years as a machinist’s tool, but they have become increasingly popular among woodworkers in recent years. A quick search reveals dozens of videos promoting these precision steel rectangles. The reason for the sudden surge in popularity is simple: they are genuinely useful shop accessories, and they have become much more affordable than they used to be.

The name comes from their precise ratio. 123 blocks are machined so that they are twice as wide as they are thick and three times as long as they are thick. A standard set might be 1 inch thick, 2 inches wide, and 3 inches long. Metric versions follow the same ratio at 25, 50, and 75 millimeters.

This guide covers what makes 123 blocks so useful, the common design flaw found in many inexpensive sets, and the hardware kit that solves that problem. It also looks at a sharpening station that brings everything you need into one portable case.

What Makes 123 Blocks Useful

The precise dimensions of 123 blocks make them excellent setup tools for a variety of shop equipment. You can use a pair of them to precisely and repeatedly set up a table saw fence at 1 inch, 2 inches, 3 inches, and so on. With the addition of common fractional spacers, you can achieve any setting in between.

Blade height can be set the same way. Because the blocks are machined precisely square, you can also check that the blade is perfectly perpendicular to the table. They work for calibrating the cursor on a fence, since you know exactly how wide each block is. You can even use one as a reference block to make repeated cuts by simply adding 3 inches to your desired fence setting. The offcuts can pile up next to the blade without kicking back at you.

The table saw is just the beginning. These blocks are useful all over the shop: the drill press, the router table, the band saw, the joiner, and more. Machinists have relied on them for generations, and woodworkers have found just as many applications.

The Common Design Flaw in Inexpensive 123 Blocks

As 123 blocks became popular with woodworkers, manufacturers focused on making cheaper versions. The goal was to create an affordable block that the average woodworker could justify buying. The result is the inexpensive version that has become widely available.

These budget-friendly blocks work well for all the uses mentioned above and more. However, many of them have a serious design flaw. The blocks are filled with holes so you can connect two or more of them together in various orientations to make precise custom jigs. Some holes are threaded, and others are smooth. The idea is that you slip a bolt through a smooth hole and thread it into a threaded hole in another block.

The problem is that during manufacturing, all the holes are bored to the same size, and then half of them are threaded. In practice, the threaded portion on the end of a bolt will not pass through the unthreaded hole. This means you cannot use the blocks as intended without finding a workaround.

One workaround is to enlarge the unthreaded holes with a large, expensive cobalt drill bit. That is not easy, since the blocks are made of very hard steel. Even if you manage to enlarge the holes, inexpensive 123 blocks often have another flaw. While the surfaces are ground flat and square, the positions of the holes may be slightly off. When you connect the blocks together, the mating surfaces might not align perfectly flush. Enlarging the holes is likely to make that problem worse.

Another workaround is to use an undersized bolt that passes easily through the holes and secure it on the other side with a nut and washer. But then the bolt heads sit proud of the surface, where they get in the way. Both of these solutions create more problems than they solve.

The Hardware Kit That Fixes the Flaw

There is a simple solution to the 123 block design flaw. A small hardware kit contains everything you need to connect blocks securely without any protruding hardware.

The kit includes three pairs of screws that correspond to the same 1-2-3 ratio as the blocks. There are also four barrel nuts: two threaded and two with enlarged threadless holes. An Allen key and a small screwdriver complete the kit, so you have all the tools you need in one handy place.

Here is how it works. Orient the blocks any way you like. For example, you can make a right angle jig to clamp to a drill press table. Run a screw through the hole in the end of the top block. Insert one of the threadless barrel nuts into the hole in the block’s face so the screw can pass through it. The slot on the end of the nut corresponds to the direction of the hole, making it easy to orient. If you need to tweak its position, the small screwdriver is there for that.

Next, slip one of the threaded barrel nuts into the lower block, where the end of the screw can thread into it. The Allen key tightens everything together. Using two screws to secure two blocks together evenly is usually a good idea. There is extra room in the holes, so you can make sure the surfaces are flush before locking everything together.

The result is a solid, precise jig with nothing protruding above any of the surfaces. You can assemble the blocks in any orientation using the shorter screws. It is a simple idea made even simpler by having all the hardware and tools in one place.

If you have a set of inexpensive 123 blocks that you like, there is no need to replace them. This hardware kit lets you keep using them without living with the frustration of useless undersized holes.

Choosing a Set of 123 Blocks

If you do not already own a set of 123 blocks, they are worth adding to your shop. They are inexpensive, precise, and useful for a wide range of setup tasks. The key is to understand the potential design flaw before you buy.

Inexpensive sets work great for all the standard uses: setting fences, checking blade perpendicularity, calibrating cursors, and making repeated cuts. The surface grinding is typically flat and square, which is what matters most for these applications. The hole alignment issue only becomes relevant when you want to connect blocks together for custom jigs.

If you plan to use your blocks primarily as setup tools, an inexpensive set is a perfectly good choice. If you want to build jigs by connecting blocks, factor in the cost of the hardware kit. Together, they still represent excellent value compared to the premium sets that cost a couple of hundred dollars.

A Sharpening Station Worth a Look

The Empower SPS sharpening station is a different kind of shop accessory, but it shares the same philosophy of having what you need in one place. It was four years in the making and is designed to provide everything you need to sharpen and strop your tools quickly, so you can get right back to work.

The system begins with three diamond plates at 300, 600, and 1200 grit. After sharpening, you switch to the magnetic stropping plates, which are color-coded to accept three levels of honing compound: 1800, 2500, and 5000.

When your tools are razor sharp, everything goes back in the case, including the compound sticks and lapping fluid. The simplicity is a major selling point. No more hunting around the shop for what you need. It is all in one place.

The portable case makes this system especially appealing for travel. If you like to carve while on the road, this is a convenient way to keep your tools sharp away from the shop. It also works well as a second system for working outside the shop.

If you are looking for a new sharpening system or a second one for travel, the Empower SPS system is worth a look.

Buying Advice

For 123 blocks, the main decision is whether you need to connect them for jigs. If you do, plan to buy the hardware kit alongside your blocks. The kit is inexpensive and solves the design flaw without requiring any modification to the blocks themselves.

For sharpening, consider how and where you work. The Empower SPS system makes the most sense if you value having everything in one portable case, whether for the shop or for travel.

Conclusion

123 blocks are a genuinely useful addition to any workshop, and the hardware kit makes even inexpensive sets fully functional for jig building. The Empower SPS sharpening station offers a similar appeal: everything you need, organized and ready to go. Both are practical upgrades that solve real problems without adding complexity to your workflow.