What are the black diamonds on a tape measure?
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I'm pretty new to DIY and am slowly filling a toolbox with some basic tools for small home repairs. I recently was looking at my tape measure when I realized I have never really looked carefully at the blade. I'm somewhat confused by all the markings on the blade and would like to know why there are small black diamonds on my tape measure.
The small black diamonds, or triangles (diamonds are more commonly found), on the top scale of the tape measure starting at 19.2 inches are for truss layouts for 8-foot sheet goods. They are also known as the "black truss" markings. They provide a quick visual for the tape user and speed up the measuring process.
Originally, 19.2 inches was used in metric layouts. Dividing 5 into 96 inches (8 feet) gives 19.2 inches, which yields five trusses per sheet. The black arrow in the photo to the right points directly at the black diamond located on 19.2".
The "red stud" markings every 16 inches allow for a standard layout of six studs per 8-foot (96") section. You will find 5 black diamonds or 6 red stud markings in an 8-foot width.
Truss Example: Look carefully at your tape and count the black diamonds. You'll notice that the fifth one lands on 8 feet. Since an 8-foot sheet spans half the distance of its size, the second course would start at the halfway point (4 feet) or, in this case, at the third diamond, which is slightly over 3' 2 3/8".
The 19.2" black truss marking is a better span if you don't want to span 24 inches on center with today's undersized plywood. However, I prefer 16 inches on center for a truss layout, especially if 1/2" wallboard will be attached to the bottom chord of trusses. Even with a 19.2" layout, I would recommend using 5/8" or 3/4" plywood and 5/8" wallboard.
Understanding the meaning of the diamonds or triangles on a tape measure is just one facet of using this complex tool.
To really learn the ins and outs of reading a tape measure and to gain insights into choosing the best one for you, consider purchasing my award-winning article, "Learn How to Read and Choose a Tape Measure." This article received the 2008 Vaughan/National Association of Home and Workshop Writers (NAHWW) Golden Hammer Writing Award in the Internet Category.
Available in both .pdf and hard copy, this 8-page article features 21 color photographs and provides outstanding information about using a tape measure to its full potential and purchasing a quality tape measure.
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Question answered by Leon A. Frechette.
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