Fiber Brush, Cleaning Pen, Hand-held
Sometimes even the smallest brush is too large to reach into tiny details on coins and artifacts... Yes or no? This hand-held tool is exactly what you've been seeking, trust me.
The size of a ink pen, there is a twister on the end that allows you lengthen or shorten the bristles to your exact needed specification. When the length is reduced to only 1-2 millimeters, I use it as a spectacular scrubber to gently remove soft dirt on dry (not wet) coins and especially on silvered issues with zero harm to your precious patina.
Before use, twist open the fibers full length, give them a few finger flicks to loosen them up, then re-close to the length needed. Very cool! This cleaning pen will last you for many years.