Tran The Van, and Nguyen Van Thanh. “A MANUFACTURING METHOD FOR GENERATING A VARIABLE-PITCH ROTOR OF TWIN-SCREW CACUUM PUMP”. UTEHY Journal of Applied Science and Technology, Vol. 17, Apr. 2018, pp. 8-13, http://tapchi.utehy.edu.vn/index.php/jst/article/view/121.