Have you noticed that the arrows you use in archery have some markings near the shaft? Those numbers mean something and it is not a batch number, a date of manufacture, or a lottery combination. These numbers are technical measurements and they can guide you on how to choose the perfect arrow for that perfect bull’s-eye.
For example, you saw the following set of numbers, 1206/370, marked on your aluminum or carbon arrows. The first two numbers determine the diameter of the shaft; hence, for the particular example, the diameter can be calculated as 12/64ths inch. The next two numbers, 06, represent the thickness of the core, and the measurement is calculated as the thousandth of the number which is 6/1000 or 0.006 inch. The last three numbers after the slash symbol is the spine deflection at 28 inches. It is calculated as 370/1000 or 0.370 inch. In summary, the marking “1206/370” means the arrow has a diameter of about 12/64 or 0.18 inch, 0.006 inch core, and 0.370 inch deflection.
Other identification markings for aluminum arrows only have the first four numbers. They still refer to measurements and here’s how: for example, you have the marking “1716”, this means that the diameter of the arrow is 17 divided by 64 of an inch, or approximately 0.266 inch, while the third and fourth number corresponds to the thickness of the wall or the tubing that surrounds the core. For the example, 16 divided by 1000 is 0.016 so the wall is 0.016 inch thick. Comparing this with other measurement, say, a 1916; a 1916 and 1716 arrows have the same wall thickness but the 1916 has a larger overall diameter. The diameter of an arrow determines how “fat” the arrow is while the wall thickness is used to gauge which arrow have stiffer spines.
The four-number notation has been used to mark aluminum arrows, however, carbon hinting arrows are marked differently. Carbon arrow users say that these arrows, instead of being classified through diameter and wall thickness, are categorized through spine deflection. Manufacturers calculate for the estimated deflection by combining the diameter and the thickness. For some brands like Beman and Easton, as the number decreases, the arrow becomes stiffer; these numbers are actual deflection of the spine. Others use numbers that corresponds to certain stiffness but it is not the exact measurement, or it can be to identify the amount of force the arrow can withstand.
The markings are there so you can easily identify which arrow is most suited to your bow. With just a single glance, you can compare which arrow has better deflection or which is thicker and heavier.