I want to purchase a set of recoil 670 F3 shafts to install in my irons. They are bought one length @ 40 inches i presume.

do i trim them to length from the butt or the tip ? as i have never done this before.

You want to tip trim each shaft per the IR6 trim code guide (different tip trim for each iron). You then butt trim each shaft for the finished club length. Also, the specs say that the uncut length of the Recoil 670 iron shafts is 41″.