Smgda 12" Combination Square Stainless Steel Adjustable Sliding Ruler & Protractor Level Measure Measuring Set 4-Piece Carpentry Tools Carpenter Square, Woodworking Tools, Metal Ruler, Framing Square

A versatile square set that punches above its price—if you understand its limits

I’ve kept a combination square within arm’s reach for most projects, but I wanted an affordable kit that included both a protractor head and a center head without feeling like a toy. The Smgda combination square set ticks those boxes. After several weeks of use in the shop—marking casework, checking joinery, laying out miters, and centering on round stock—I’ve formed a clear picture of where it shines and where it asks for patience.

What’s in the set

• 12-inch (300 mm) stainless steel rule with laser-engraved metric and imperial graduations
• Square head with integrated spirit level and a tucked-away scriber
• 180° protractor head
• Center head for finding the centerline on round or square stock
• Reversible lock bolts to clamp each head to the rule

That combination covers most of what I need day to day. The square head handles 90° and 45°, the protractor lays out arbitrary angles, and the center head earns its keep more often than you might expect—especially for dowels, pipe, and turnings.

Build quality and feel

The stainless rule is thin but not flimsy, with crisp, deeply laser-etched markings that haven’t smudged or faded. The heads are aluminum alloy with steel lock hardware. Out of the box, all parts were free of burrs, and the rule edges were straight and clean. The lock bolts are knurled and easy to grip, and the sliding action is functional—though not silky. There’s a slightly gritty feel to the slides until you clean the rule and run them a few times with a drop of light oil. After that, they move smoothly enough for consistent clamping.

This isn’t a tank-like, heirloom machinist set. It’s lighter, and the heads don’t have that densely milled feel of a premium brand. But the materials aren’t junk either. The stainless rule resists rust in a humid shop, and the heads have held up to normal handling and clamping pressure without deformation.

One small note: the hardware that retains each head can be disassembled completely. That’s convenient for cleaning, but don’t back the bolts off over the edge of the rule unless you’re prepared to catch the spring and nut. It’s not a flaw so much as a quirk—worth knowing so your parts don’t scatter across the bench.

Accuracy and calibration

Before putting it to work, I checked the square head against a known reference square using the flip test. It was acceptably square out of the box; any error was too small to register in a 300 mm scribe. The 45° fence was also close. If you do find a discrepancy, you can calibrate: lightly loosen the lock, nudge the head along the rule as you hold it firm to a reference edge, and retighten. The lock bolts clamp with enough force to keep settings from drifting during use.

The protractor head is usable but more sensitive to technique. There’s a touch of play before you snug the lock. The fix is simple: always approach your angle from the same direction to take up any slack, then tighten firmly. If you do that and mark with a knife or sharp pencil, the layout is accurate enough for general woodworking and light fabrication. For close-tolerance metalwork, I still reach for a dedicated bevel gauge and an angle block.

The center head is spot-on. Finding the center of a dowel or pipe is as quick as two intersecting marks, and the V-face references cleanly. I used it repeatedly on 1-inch oak dowels and aluminum round stock with no slippage.

Day-to-day use in the shop

The square head is the star here. For cabinet parts and furniture components, it’s been stable and confidence-inspiring. The rule locks in square without creeping, and the integrated spirit level is handy for quick “good enough” plumb checks on installations, though I don’t treat it as a substitute for a proper level. The hidden scriber in the square head is genuinely useful when I misplace my marking knife; it’s not razor-sharp, but it’s always there and it saves a trip across the shop.

The 12-inch length is ideal for bench work and small to medium assemblies. For framing or sheet-goods breakdown, I’d still reach for a longer straightedge or a speed square. I do wish there were a small pencil notch near the rule end for quick parallel marking—a convenience on some squares that’s missing here. Workaround: use the scriber or a marking knife against the square head; both give a cleaner line than a pencil anyway.

On the metal side, the stainless rule holds up to scribing and light layout ink without scratching or lifting the markings. I’ve used it for setting fence offsets on a drill press and verifying small miters on aluminum angle with no surprises.

Protractor head: usable, with the right technique

It’s tempting to treat a combination square’s protractor like a precision angle tool. Don’t. This head is functional for layout and quick transfers, but it’s not a metrology instrument. There is a little clearance between the rule and the head. The key is consistency: preload the head in one direction, tighten the lock bolt, and verify against a known angle if the project demands tight accuracy. With that routine, the protractor was perfectly fine for laying out chair rake and splay, mitered aprons, and simple bevels.

If your work depends on repeatable sub-degree angles, invest in a dedicated digital angle finder or a higher-grade bevel protractor. For everyone else, this gets the job done.

Center head: surprisingly handy

This is the sleeper hit of the set. I used it to find centers on dowels for plugs, mark drill points on copper pipe, and split 1x stock for decorative grooves. It’s fast, intuitive, and accurate. The V-groove nests firmly, and the rule doesn’t slide when clamped. If you haven’t used a center head before, you’ll adopt it faster than you think.

Markings and readability

The laser-engraved graduations are clear and consistent on both metric and imperial scales. Contrast is good under normal lighting. Under very bright, direct light, the stainless can glare a bit, but it’s not difficult to read if you adjust your angle. The rule edges are square and clean, making it reliable as a straightedge for scoring.

Limitations and nitpicks

• The rule is on the thinner side. It’s accurate and straight, but you can flex it slightly if you bear down. Treat it like an instrument, not a pry bar.
• The sliding action arrived slightly stiff/gritty. A quick clean and a dot of oil improved things substantially.
• The protractor head has some play until tightened. Use consistent technique and verify for critical angles.
• Accessories don’t “park” anywhere when not in use. I keep the extra heads in a small pouch so the hardware doesn’t walk off the bench.
• No pencil groove at the rule tip. Not a dealbreaker, but I miss it for quick parallel lines.

Tips for best results

• Clean and lightly oil the rule before first use to smooth the slides.
• Preload the protractor head from one direction before locking your angle.
• Check squareness with a flip test and, if needed, calibrate by nudging the head while clamped to a reference edge.
• Use the integrated scriber for crisp lines—especially on end grain—when a pencil feels too blunt.
• Don’t fully unthread the lock bolt off the rule unless you’re ready to catch the spring and nut.

Who it’s for

This set suits woodworkers, DIYers, and light metal fabricators who want a full-featured combination square at a reasonable price. It’s accurate enough for furniture and cabinetry, cabinet installs, and general shop layout. If you’re a machinist chasing thousandths or a finish carpenter who needs bulletproof angle repeatability on site every day, you’ll want to step up to a premium square and a dedicated protractor.

Recommendation

I recommend the Smgda combination square set for budget-conscious users who want a capable, all-metal kit with a useful center head and a serviceable protractor. It’s accurate where it counts, the markings are clear, and the square head locks reliably. You’ll trade a bit of refinement—the protractor demands consistent technique, the slides benefit from a little tuning, and the rule is on the lighter side—but none of those issues kept me from using it daily for layout and verification. For the price, it delivers real utility without pretending to be a precision instrument. If you understand its limits and work within them, it’s a solid addition to the bench.