The Tombow Mono Zero mechanical eraser is available in both rectangular and circular sizes.  This pen-type precision eraser enables detailed modifications and adjustments in painting, highlighting, sketching, and more, without generating waste. 
The rectangular size measures 2.5 x 5 mm, while the circular diameter is 2.3 mm. The eraser is refillable and reusable. You can prepare additional rubber replacement cores and easily swap them out when needed, without affecting your creative process.