Socket set screws are a headless fastener which usually sits flush or just below the surface of the application.  They are designed to secure pullys or machine parts to shafts.  Cup point set screws dig into the contact surface for a secure connection.  Flat, oval, and soft-tip set screws are used for minimal contact of the surface for a wide range of applications.  Extended-tip (Dog Point) set screws have an extended tip allowing it to fit into a mating hold or slot.  Cone point set screws have a pointed tip allowing it to grab into softer materials like brass.  Swivel tipped set screws allow for a constant connection with  an angled or uneven surface.  There are a variety of materials on socket set screws including alloy steel, stainless steel, brass, and nylon.