Center finder marking gauge
A center finder lays two angled legs against the edges of a board so a pencil dropped through the middle hole scribes a line exactly down the center, whatever the width. The tool is a flat V shape about 120 mm across with legs at 45 degrees, a 3 mm pencil hole at the apex and a 20 mm central slot for stock up to 60 mm wide. Add 0.5 mm chamfers so it slides smoothly, and print it flat in PLA or PETG.
Rather than settling on a gauge that only handles the widths someone else needed, tell SpeakCAD the widest stock you work with and the pencil you use. The geometry is regenerated to fit, and you can request a second slot for offset lines right in the conversation. Previewing the design is free and needs no installation.
Model a center finder marking gauge: flat V-shaped body 120 mm wide, 60 mm tall, 8 mm thick, legs at 45 degrees, a 3.2 mm pencil hole at the apex, a 4 x 20 mm center slot, and 0.5 mm chamfers on all edges.