RE: spine
The number re: spine depends on the manufacturer. With PSE and Carbon Express the higher numbers are stiffer. Easton and Gold Tipare the other way. Higher numbers are weaker spine. With aluminum it's different from carbon. You have to consider the shaft diameter (first 2 numbers) and wall thickness (last 2 numbers). A 2413 is 24/64" in diameter with a .013" wall.