Precision Brush - Inside Diameter of Inside Coil Brush

The ID or "Inside Diameter" of an inside Coil Brush is measured by taking the OD less the Overall trim length of the strip brush times 2. Depending on the brush you may be able to measure it from the filament tips to the filament tips, but sometimes this is not always possible, especially with small Inside Diameters. The filaments tend to swirl on the Inside of the brush if there is not enough room for all of them which is the nature of this product.