The PING i3 irons come in two versions an oversize (OS) set and a blade set. The OS set has larger heads that make the irons more forgiving and easier to hit consistently. The OS irons also have more offset to help square the clubface at impact. The blade set has smaller club heads and less offset to allow more control for better golfers. Both sets feature a Custom Tuning Port in the cavity to reduce unwanted vibrations for an improved feel.