In 20 years as an audio-repair bench tech, I used "scratch brushes" almost every day to clean metal chassis and the contacts of switches and tube sockets and what not in preparation for soldering, or to remove solder mask (aka solder resist) from a circuit board trace. Several things I forgot to mention: some of the cheap Asian made scratch brushes sold online do not necessarily allow you to change the fiberglass brushes when they wear down because the brushes may have been glued and heatshrinked into the tool. The better quality scratch brushes such as the EuroTool brand you see here do allow you to change the brushes (hard to imagine that you would wear out a steel or brass brush, but the glass ones do break off in the form of little bristles and eventually wear down beyond the point of being able to extend out from the tool). Also, if the end of the fiberglass brush is worn, soft, and splays out a little too much, you can stiffen the bristles with a dab of superglue (water thin Superglue is preferable). Amazingly, the fiberglas bristles last longer and break off less, not more, if used in the battery powered tool! Finally, it's important to note that broken off bits of nearly invisible glass fiber can get stick in your fingers where they'll pain you for days until they work their way out; you can try using a piece of extremely sticky tape to remove them, but otherwise, especially if you are a gigging musician, you should wear light gloves (though I've never bothered to, since I'm a shit player and don't gig).

I purchased the EuroTools scratchbrushes from Esslingers' watch/jewelry repair-supply; they do sell the cheaper, lower quality type as well (and they sell abrasive-rubber polishing wheels, Dremel style bits that appear as if they might be useful). The wood-stick draftsman's erasers I show here are particularly useful for polishing silver-plated contacts inside relays, switches and potentiometers; I'll have to do a more specific video about those. My apologies for my halting speech and for handling things outside of camera range; I did this live with a smartphone, no script, no rehearsal, and a bench-clamped phone holder that is sub-optimal. "Do What Thou Wilt"!