This item is a traditional Japanese woodworking tool called a sumitsubo (literally "ink pot"), used to snap straight lines on wood just like a modern chalk line.
How it works: A silk thread is spooled around the wheel, passes through the inkwell, and gets soaked in black ink. The carpenter pulls the thread taut, plucks it, and leaves a perfectly straight, fine ink mark.
Design & Craftsmanship: Historically carved from solid wood (often Japanese elm or keyaki), sumitsubo were highly personalized and often served as a master carpenter’s most ornate tool.
