Wood screws are meticulously designed for fastening wood to wood. As you can see, there is an unthreaded portion between the head and the aggressive thread shank. This part is used to slide through the top board so that it can be pulled tight to the board being attached. Thanks to the threaded shank, wood screw can offer a greatest holding power during the connection. To match the various tools, there are seven head types for choice, including llips flat head, frearson flat head, slotted flat head, slotted oval head, llips round head, slotted round head and square flat head.