Have to know what size montecs you've got. 85, 100 or 125?

It's not confusing figuring out what size arrow to use. It's based on the performance of your bow (hard cam, medium cam, etc), draw weight, draw length, arrow length and broadead weight. Many outfits have arrow selection programs where you simply plug in your information and it spits out what size you need. With carbon arrows, it's that easy.

The only thing you really need to keep in mind is, if you wind up right on the cusp between one size and having to go to the next stiffer size, it's always best to go ahead and move up to the stiffer one.