Don't forget that arrows come in hundreds of wall weights (schedule??) and diameters. A large diameter thin wall would be quite a bit weaker than small\ thick one. If I remember correctly the numbers are something like 2214, the 22 is the diameter and the 14 is the gauge of the aluminum.
Yup, Aluminium arrows sizes are identified with 4 numbers printed on the shaft*such as 1816. This means the arrow has an outside diameter of 18/64" and a wall thickness of 20 one thousands of an inch.