The old fence posts many hunted with...still have some around...lol
Easton aluminum arrows measures thus
The four-digit number refers to the outside diameter and wall thickness of the shaft. The first two numbers are the outside diameter in 64ths of an inch. The second two numbers are the wall thickness in thousands of an inch. For example, a 2413 shaft would be 24/64th of an inch in diameter and .013 of an inch wall thickness. OD and wall thickness are the two variables in controlling spine for aluminum arrows.
Or 24/64 inches =9.525 MM
OR 2413 = 9.525 mm wide
Neil