Replaces the following part numbers

McCulloch 300110, 300639

This fits a lot of the McCulloch "Curved" Shaft Trimmers that DOES NOT have a bumb knob that screws on.Just a cap that you twist off, the head is held on by a star washer that you have to break off with a screw driver in order to remove the old head. the new head comes with a new star washer that grips the solid 3/8 shaft and holds the head in place. NOTE if your shaft is hallow with threads then you need to order catalog # 9598