People are only just realising why there are diamonds on tape measures

If you’ve ever looked at your tape measure in detail, you may have noticed the black diamonds printed between 19 and 20 inches. This is something that is printed on every tape measure, but not many people actually know why this is.

Over the years, people have turned to Reddit and Quora after becoming curious about the origins of these diamonds. Taking to the tools subreddit, one Reddit user wrote: “What is this black diamond on my tape measure, appearing a fraction of an inch after 19 inches and multiples thereafter?” To which another user replied: “The diamond-shaped marks on a measuring tape are called truss marks or black diamond markings.

“They are spaced every 19.2 inches and are mainly used in construction for laying out floor joists, roof trusses, or wall studs evenly across an 8-foot span. Why 19.2 inches? An 8-foot section = 96 inches 96 ÷ 5 = 19.2 inches.

“This spacing allows 5 supports per 8 feet, which can reduce material while still meeting some structural requirements. You’ll usually see the diamonds at: 19.2″ 38.4″ 57.6″ 76.8″ Most residential framing still commonly uses: 16-inch on center (16″ O.C.) or 24-inch on center (24″ O.C.) But the diamond marks help when using the 19.2″ layout system.”

While a second added: “Many have already pointed out the math, but adding some history here because this is one of my favourite pieces of construction trivia. Diamond layout was invented based on the engineering allowed by using wooden I joists.

“These new joists were more expensive than traditional solid sawn lumber so they were sold with diamond layout on the idea that requiring one less joist per 8’ sheet helped offset some of the cost when switching to their product.

“Additional, wooden I joists were pioneered by Trus Joist Inc in 1969, which is why many builders refer to all such products as ‘TJIs’ in the same way many refer to any tissue as a Kleenex.”

Similarly, a DIY expert recently took to TikTok to explain why tape measures have a metal tip that moves slightly. Posting on Tool Talk TV’s social media page, the expert urged people to “get rid” of their measuring tapes if the metal end doesn’t move.

He added: “All the ends on the end of the blade of these tape measures move. This is by design. So whether you’re measuring against something, or measuring away from something, that small movement in the tip allows you to get true zero.”