Most firearm owners will recognize this nylon bristle brush, especially if they’ve been in the service — the brush is included as standard issue with all M16s in the military. One end is a normal toothbrush and the other end has a very thin version of the same brush. This narrow brush will enter most of those smaller areas to get them squeaky clean.
I personally keep two of these brushes in the shop: one in the parts washer and another in the toolbox. The brush is made by many manufacturers, but I believe the Kleen-Bore is the most popular commercial version.
Street pricing starts at $2.