Socket set screws, also known as grub screws, have no head and are typically tightened or loosened with a square or hex key. A slotted set screw can be adjusted with a screwdriver. Socket set screws prevent movement of a pulley or similar machine part relative to a shaft. A cup point set screw has a rounded tip that grips and resists deforming the shaft surface. A flat point screw provides more contact with the shaft.