I finally picked up a pec double square last year after realizing my old plastic speed square was about as straight as a wet noodle. For a long time, I didn't think I really needed a "fancy" square. I figured that as long as it looked close enough to ninety degrees, the wood would just behave itself. I was wrong, of course. My joinery was a mess, and I was spending way too much time sanding down gaps that shouldn't have been there in the first place.
Once I started using a proper tool, everything changed. There is something satisfying about a piece of precision-ground steel that just clicks into place. It's not just about the accuracy, though that's the main point; it's about the confidence you get when you're marking a line or checking a fence. You don't have to second-guess yourself.
Why the Double Square Beats a Combo Square
Most people start their tool journey with a combination square. You know the one—it has the 45-degree angle on one side of the head and a 90-degree on the other. They're great for general carpentry, but in a tight workshop setting, the pec double square really shines.
The main reason is the head design. Since the head is symmetrical and only does 90-degree angles, it's much smaller and more balanced. If you're trying to check the inside of a small drawer or set the height of a router bit in a cramped space, that bulky 45-degree shoulder on a combo square always seems to get in the way. With the double square, you can flip it around, slide the blade to either side, and get into corners that would otherwise be a nightmare to reach.
Also, because it's more compact, it fits in a shop apron pocket way better. I find myself carrying my 4-inch model around all day. It's light enough that I forget it's there until I need to check a quick measurement or square up a mark.
The Secret of the Cosmetic Seconds
If you've been hanging around woodworking forums for more than five minutes, you've probably heard people talking about "blems." This is where the pec double square becomes a legendary value. PEC (Products Engineering Corporation) sells tools that have tiny cosmetic flaws—maybe a scratch on the chrome or a slightly wonky paint job on the logo—at a massive discount.
I'll let you in on a secret: you usually can't even find the blemish. I bought my 6-inch square as a "second," and I spent twenty minutes looking for the defect. I think I found a tiny pin-prick of a scratch on the back of the blade. That's it. It doesn't affect the accuracy at all. The tool is still dead-on square, the graduations are crisp, and the locking mechanism is smooth. For a hobbyist on a budget, this is the absolute best way to get professional-grade precision without paying the "Starrett tax."
Choosing the Right Size for Your Work
When you're looking at getting a pec double square, you'll usually have to choose between the 4-inch and the 6-inch versions. It's a tough call, and honestly, most people end up with both eventually.
The 4-inch model is the king of precision for small tasks. If you're doing dovetails or small jewelry boxes, the 6-inch can feel a bit cumbersome. The 4-inch is also great for setting the depth of cut on your table saw or checking the squareness of a chisel grind. It's just so nimble.
On the other hand, the 6-inch is probably more versatile if you're only going to buy one. It's long enough to bridge most gaps and check the squareness of 2x4s or larger furniture components. It feels a bit more substantial in the hand, which some people prefer. Personally, I use my 4-inch about 70% of the time, but when I need that extra two inches of reach, nothing else will do.
Understanding the Graduations
One thing that confuses people is the "4R" or "16R" markings. Most woodworkers prefer the 4R graduations. This means the blade is marked in 8ths, 16ths, 32nds, and 64ths. It sounds like a lot of tiny lines, but PEC does a great job of making them deep and easy to read. Even in a shop with slightly dim lighting, I don't find myself squinting to see where the 1/32nd mark is. The etching is permanent, too—it's not just printed on the surface, so it won't rub off after a few years of heavy use.
How I Use It Every Day
It's funny how many uses you find for a pec double square once it's sitting on your bench. It's not just for drawing lines. Here are a few ways it has made my life easier:
- Setting Blade Heights: I slide the blade out to the specific height I need, lock it, and then raise my table saw blade until it just kisses the bottom of the ruler. It's way more accurate than trying to eye it up against a tape measure.
- Squaring Up Equipment: I use it to make sure my drill press table is actually 90 degrees to the chuck. I also use it to check the fence on my jointer. If that fence is off by even half a degree, your glue-ups will be a disaster.
- Marking Mortises: If I need to mark a consistent distance from an edge, I lock the blade at the measurement and use the head of the square as a fence. I just drag the whole thing along the wood with a pencil held against the end of the blade. It works like a mini marking gauge.
Maintenance and Care
Since these are made of hardened steel, they can rust if you don't take care of them. I live in a fairly humid area, so I've learned the hard way that you can't just leave your pec double square sitting on a damp workbench overnight.
I keep a small rag with a bit of machine oil or Boeshield T-9 nearby. Every now and then, I'll give the blade and the head a quick wipe down. It keeps the sliding action smooth as butter and prevents those annoying little orange spots from showing up. If you do get a bit of surface rust, don't panic. A little bit of fine steel wool and some oil will usually take it right off without hurting the accuracy.
Also, try not to drop it. I know that sounds obvious, but a drop onto a concrete floor can knock any square out of alignment. If you do drop it, you should check it against a known "dead square" surface or use the line-reversal method to make sure it's still true.
Is It Worth the Investment?
You can go to a big-box store and buy a cheap square for ten bucks. It might even be square for the first week. But the problem with those cheap zinc-cast heads and thin aluminum blades is that they just don't last. They warp, the locking nuts strip out, and the markings fade.
Spending a little more on a pec double square is one of those "buy once, cry once" situations. It's a tool that your grandkids could probably use. There's no plastic to crack and no electronics to fail. It's just solid engineering and high-quality materials. When you consider how much wood you'll save by not making mistakes, the tool basically pays for itself in a year.
I've found that having better tools actually makes me want to spend more time in the shop. There's less frustration. Everything just fits together the way it's supposed to. If you're tired of "close enough" and want to start making things that are actually square, this is probably the best place to start. It's not flashy, and it doesn't have any bells or whistles, but it does its one job perfectly every single time.