Use for inking to trace hollow lines. It g gives the model a three-dimensional feeling and makes it appear more realistic. The effect is stronger when you choose the color to ink according to the color of the model parts. In general, you can use black for dark parts, grey for lighter parts and brown for red parts.
Gundam Marker Black (Fine)
GSI Creos Mr. Hobby GM01 Black Fine Point Gundam Panel Line Marker
GSI Creos Black Fine Point Gundam Marker GM01 – USA Gundam Store
Detail Pens & Markers - Paint, Decals, Mask & Accessories
If you're looking for the simplest way to panel line your Gundams and other model kits, look no further! Just draw in the panel lines with this marker
GM01 Black Fine Line Marker
Gundam Marker GMS113 Real Touch Marker #2 Set of 6
Mr.Hobby® GM01 GUNDAM MARKER PEN TYPE FOR PANEL LINE (BLACK) – VCA Gundam Singapore
Bandai Gundam Marker Fine Line (Black) [BANGM01] - HobbyTown
Gundam Markers 3 Black, Brown & Grey extra Fine Tip / for Panel Lines Uk
Metallic Model Gundam Markers - 6 Piece Set, Hobby Lobby