K groove, innovated by HOPO company, is a new profile structure for casement window, that has been widespread in many countries. The main feature of K groove system is to enlarge the dimension of the frame groove. In this case, frame groove of casement window needs no processing for mounting heavy friction hinges. The anti-wind-load capacity of locking systems and the max. load capability for the hinges will be greatly enhanced if the K groove structures are applied to profiles for inward opening windows and swinging doors. The invention of K groove is targeting on quality and security improvement for the whole window and door systems, as well as improving efficiency and effectiveness for fabrication.