Most people know a measuring tape is used to measure lengths and distances. But have you ever noticed the small black diamond symbols that appear at regular intervals along the tape? These markings are not decorative—they serve a very practical purpose in construction and carpentry.
What Are the Black Diamonds?
The black diamonds, also called truss marks or black truss indicators, are usually spaced 19.2 inches apart. They help builders indicate where to place floor trusses or joists when dividing an eight-foot span into five equal parts. This spacing allows for efficient use of materials while maintaining structural integrity.
Why 19.2 Inches?
The spacing comes from the “eight-foot rule” in construction:
Eight feet = 96 inches
96 ÷ 5 = 19.2 inches
Placing supports every 19.2 inches ensures that five evenly spaced supports fit perfectly across an eight-foot section, which aligns with standard sizes of building materials like plywood and drywall.
Benefits of Black Diamond Markings
Using these markings provides several advantages: