Free tools for labeling watch 3D models include Blender (with built-in annotation features) and MeshLab (for metadata tagging).
Blender lets you add visual labels (text, arrows) to watch parts like dials or straps for design notes, while MeshLab attaches structured data (e.g., material types) to model vertices or faces.
For beginners, start with Blender’s "Annotation" tool—it’s intuitive for marking specific details (e.g., crown position, strap attachments) without complex setup.