I know I'm not the only one that uses pencil for panel lining. 0.2mm mechanics pencil. Lighter than accent liner with a metallic finish. Try it sometime! : r/Gunpla
Gunpla Tutorial : Weathering Effects with Pencils - YouTube
Amazon.com: GSI Creos Gundam Marker Black Liner with Mechanical Pencil Sharp, 0.3mm : Office Products
RARE! Mobile Suits Gundam ZZ Elpeo Ple Plastic Pencil Board Pad Shitajiki 1 - Japanimedia Store