Tombo. What a beautiful word. In Japanese, it means dragonfly. The Japanese also named a delicate little potter’s tool after it that is used to gauge the depth and width of a wheel-thrown piece of pottery and facilitate throwing multiple forms of the same size. My first tombo was made from two pencils joined together with masking tape in the form of a cross. Nothing like an elegant dragonfly and it was not adjustable. Recently I came up with a better, adjustable, 30-second solution.
First, acquire a couple of bamboo chopsticks or two lengths of thin dowel. Next, make a trip to an orthodontist’s office and ask for some of the small rubber bands used on braces (or steal a couple from someone with braces) (1). The place I went to gave me two packages of 50 heavyweight bands, just for asking. Once you have the sticks and bands, assemble them by laying one chopstick perpendicularly across two stretched bands, then thread the other through the two loops, and over the first chopstick (2). The bands will allow you to easily adjust your new tool for both depth and width by sliding them in the direction needed.
To use, hold the tombo on the end of the vertical stick, above a wheel-thrown form and lower it until the point of the tool is just touching the center of the form. Maintaining the center position of the vertical stick, slide the horizontal stick left and right, then adjust its height so that the free end just touches the outer wall of the form (3). Your tombo is now ready to be used as a gauge to make multiple forms of the same size.