US Patent 7090453 Screw

A screw which can be more quickly screwed into a work piece and has better chip-exhausting effect. The screw has a rod body and higher thread and lower thread formed on the rod body. On a conic section of the screw, a cutting thread with another guide angle larger than the guide angle of the lower thread directly extends from the lower thread. Accordingly, the lower thread of the screw has better cuffing, drilling and chip-exhausting function. Alternatively, the screw can have single thread or double threads with equal height. On a predetermined section of the rod body of the screw, a cutting thread with changed guide angle is directly formed as a part of the thread to achieve better cutting, drilling and chip-exhausting function.