[SHOP: Breakaway Roping Essentials]
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The diameter of breakaway and calf ropes are measured in millimeters. According to 60-year, rope-making veteran Dub Grant of Dub Grant Rope Co., "Those ropes are made over in Japan. They’re twisted over in Japan, so they use the metric system. So a 10.0 is about like what we would call a 3/8."
That's 3/8 of an inch—the "typical" size of a team roping rope, for instance.
Decoding Rope Sizes
Grant's most popular breakaway rope, the Gold 4-Strand Poly Calf Rope (listed as #3 on the site), is available in four different sizes: 9.5, 10.0, 10.2 and 10.5, and he explains the differences as such:
"A 9.5 is like a 3/8 scant. And a 10.0 is about the size of a 3/8. 10.2 would be about like a 7/16 scant. And then a 10.5 is about like a 7/16 full. And, the bigger diameter they are, the little more heavy they are."
Scant and Full?
In roping measurement lingo, "scant" means a little bit less than. So, a 3/8 scant means the diameter of the rope is slightly less than the typical 3/8 rope size, usually coming in at 5/16 ... 1/16 smaller than 3/8.
"Full," on the other hand, means true. A full 3/8 is exactly that: 3/8.
Rope Size Breakdown
So, now that you know the lingo and the numbers, how do you know which is right for you? Grant breaks it down:
"The 9.5 is what most young kids use and some of the smaller ladies. Then, the 10.0 would be next, for ladies in high school and out of high school, and in college—most of them use a 10.0. Now, when you get up to a 10.2, that's getting into what most men and boys use to rope calves with. A few girls do, but not many. And then the 10.5, that’s mainly for men to rope calves with."
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