Well, I'm no expert but from my experience limbs built for the standard and extreme risers are all compatible with each other. Even from RH to LH risers. Limbs that are rated for a standard riser will be 3#'s heavier on an extreme riser and vice versa. I think it all changes when you go to the newer riser designs like the SXT, ZSR and Nitro. I know Nitro longbow limbs won't work on a standard or extreme riser because I talked to Bill about it not too long ago. Hope that helps somewhat.