I can' t believe you found a shop that didn' t try to set you up with carbons from the outset.[]

Easton' s aluminum arrow sizes are pretty straight forward, but you have to have a chart to find out what spine (stiffness) they are.

Some carbons tell the spine range on the shaft, like GoldTip sizing a shaft 5575. That means a 29" arrow will work for bows between 55 and 75 pounds draw.

Some carbon manufacturers number their sizes by the amount of deflection they show on a spine tester. Some seem to grab a number out of thin air to put on their shafts. You have to use a chart to pick the right arrow for those two systems.

All the arrow manufacturers have their spine selection charts on their websites.