The tip and butt diameters are the outside dimensions of the tip and the butt of the shaft. Wood shafts have tip measurements of .355". Wood heads have corresponding inside measurements of .355". Iron heads and iron shafts have .370" measurements that fit together. Butt sizes are indicated to help with your choice of grips. Almost all grips available will fit on butt sizes ranging from .560" to .620". Big butt shafts have big butt grips that fit them.