Leader Math (or, the Mystery of “X”)

In the U.S. leader and tippet material diameters are typically measured in thousandths of an inch, with tippets also given an additional “X” designation. An example of each that you might see on a spool of tippet material would be as such: .006” (read as “six thousandths”) and 5X (read simply as “five x”). The X designation has a relationship to the thousandths diameter.

This is where the old “Subtract from Eleven” rule comes into play. This rule gives you a simple way to determine thousandths diameter or “X” designation of a section of tippet material, as long as you have one of the two numbers. The baseline for this rule is 0X, which is .011” (eleven thousandths). To get either “X” or thousandths subtract the other number from 11. When doing the math, it initially helps to view the thousandths diameter sans decimals. In other words, a diameter like .011” simply becomes “11.”

Let’s apply the Subtract from Eleven rule on the baseline tippet above, which was identified as 0X or .011”. Here is the math to determine the X designation if you know the thousandths diameter: 11 – 11 (that’s .011”) = 0. That “0” corresponds to 0X. Here is the math to determine the thousandths diameter if you already know the X designation: 11 – 0 (that’s 0X) = 11. That “11” corresponds to .011”.

To expand the idea, here are two more examples (we’ll use .006” or 5X): 11 – 6(.006”) = 5(X), or 11 – 5(X) = 6(.006”). Run through the rule a few times and you will have it.

And to finish, here’s a quick look at the typical U.S. tippet sizes with the X designations and corresponding thousandths: 0X (.011”); 1X (.010”); 2X (.009”), 3X (.008”); 4X (.007”); 5X (.006”); 6X (.005”); 7X (.004”); 8X (.003”).

How might all this be useful? Try here to start.

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