Black Friday: lifetime access is on a special offer in the app, until November 30. Black Friday: special offer on lifetime access, until November 30. Download
웜 톱니바퀴는 기계에서 힘을 전달하는 데 사용됩니다.weom topnibakwineun gigeeseo him-eul jeondalhaneun de sayongdoemnida.The worm wheel is used to transmit power in machines.