Spine and arrow weight are apples and oranges. Spine refers to stiffness, and weight is the overall weight in grains. Most shafts carry a gpi (grains per inch) designation. To that you add the weight of the nock, inserts, fletching, wraps, and point. And the spine is not so consistently quantified- some arrow makers call the 50/65, 60/75, etc; referring to the draw weight of the bow. Others (like Easton) list them as 500, 400, 340, and 300 - indicating the deflection of a 28" shaft when a 1.94 lb. weight is hung from the middle. There are some really good charts to help you select the correctly spinedarrow shaft.