This screw retains body pins 120 and 121 on your KWA KM4, and installs onto the left side of the receiver.
This replacement part is displayed as number 138 on F90 diagram
The I-25 e-clip fits multiple KWA models, and appears on respective diagrams as M11A1 NS2 part 104, KM4 Series part 242, RM4 part 242, and LM4 PTR part 209.