Needing to clean banana jacks in a vintage Simpson 260, I whipped up this tool. The basic brush is a gun cleaning brush with bronze bristles. Made by Outers for a .17 caliber rifle. It has 5-40 threads and is their number 41972, $1.67 at Wallyworld. It worked held in pliers and wet with DeoxIT from CAIG, but its much handier with a handle. My handle is made of 1/2” aluminum rod but wood or plastic would work too. It should work equally well on SO-239. I shoved it in then rotated it clockwise. It would be a good idea to always turn it clockwise after the bristles have been laid to one side. Turning it backwards will cause it to bind up and to crush the bristles so they won't work as well as they did at first.

The raw material.

The tool.

Similar brushes are on the hooks in various sporting goods departments and stores for sizes up to near 7/8” for larger connectors. Probably McMaster-Carr has smaller brushes, but doesn't deliver on Memorial Day for $1.67