I went to my local big box store this past weekend to find a replacement for my lawnmower blade (it's a Craftsman Precision Plus if that makes a difference, but it shouldn't).
When I got to the lawnmower blade section, I was impressed to find about 50 different sizes, although they all looked to be the same length.
However, despite very little variance in length, some were billed as being "42 in." (inches?) while others were billed as "21 in.". Although some were definitely longer than others, the variance was no more than a few inches. No way one was actually 21" and another was 42".
How do blade sizes work? Is "21 in" actually 21 inches? If so, how does that explain variances of only a few inches?