# Do You Know the Purpose of Mysterious Black Diamonds on Measuring Tapes?

June 14, 2019 Updated: June 24, 2019

Many people doing DIY home-building, repair, or remodeling projects use tape measures all the time. But even these semi-pros might not know all the incredible things this ordinary tool can do for you.

So today, we’re going to take a closer look at your tape measure and help you do five things with it that you probably didn’t know you could!

Before we get to all the cool things that are built into your tape measure, take a second to look at one. While the untrained eye might just see the big black numbers indicating inches and the smaller black markings indicating halves, quarters, eights,and sixteenths of an inch, there’s a whole lot more going on.

1) The Black Diamonds

Perhaps the most mysterious of all the markings on your tape are black diamonds or circles. Look closer and you’ll see they appear at 16 inches and again at 19.2 inches. What could be the point of these?

The answer is two of the key elements for building a house: studs and joists

Most building codes mandate that studs be spaced 16 inches apart, so the tape will help you stay on the right side of the law as you construct (as well as making sure your wall can safely bear the load it needs to).

Joists on the other hand should be 19.2 inches apart. Since plywood often comes in 8-feet sections, you’re in luck. Divide 8 feet (or 96 inches) by 19.2 and you get 5. Thus, one sheet of plywood will cover 5 joists and you won’t have to do any cutting. Pretty nifty, huh?

2) Roman Numerals

You’ll often see the roman numeral I or II on your measuring tape, sandwiched between the 11- and 12-inch markings. This is to tell you what kind or “class” of measuring tape you have. While class I are most accurate and used by professional builders because of their incredible accuracy, your average household tape is probably class II, and thus slightly less accurate. However, the deviations are so small it won’t matter for most home projects.

Beware if you have a class III tape, as this means it hasn’t been tested for accuracy and could lead you astray in your measurements and leave you with a door that never quite closes or a wonky fitting that doesn’t look right.

3) The Measurement on the Tape Measure Housing

Let’s say that you’re measuring inside a tight space like a windowsill, where there’s no extra room for you to pull your tape out and get a full reading. Look on the back of the plastic or metal housing of your tape measure. There you’ll see a measurement, which is none other than the length of the housing itself.

Just add this to whatever you had on the tape itself and you’ve got it. A nifty trick that you could save you a lot of time and head scratching.

4) The Serrated Edge or “Teeth” on the End

You might have noticed that the end of tape has plastic or metal “teeth,” maybe even by scratching yourself accidentally. Well, the reason those guys are sharp is that your tape measure manufacturer knows what life is like.

Ever started to do a measurement only to realize a pen or pencil is nowhere in sight? Simply push down the serrated edge into the wood or wall you’re working on, and it will leave a handy little marking so you can find it again when you need to.

5) The Moving Hook on the End

Last but not least, you’ve probably noticed that the hook on the end will move ever so slightly if you pull it. This is because the last 16th of an inch is missing on the tape. That’s exactly how long the hook itself is, so if you’re measuring flush you know exactly what you’ve got.

There you have it. So the next time you get your tape out, remember there’s a lot more to it than meets the eye.

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