Kratzbürste

I've been using this to prep old copper pipe fittings for soldering, and the retractable metal bristles are perfect—adjusts just like a mechanical pencil to keep the tip fresh. It removes tarnish and paint effortlessly without scratching the surface underneath.

The bristles are stiff enough to actually scrape off stubborn oxidation on copper, and the retractable design means I don't have to worry about them getting bent in my toolbox. It preps surfaces in seconds, which beats scrubbing with sandpaper every time.

Finally got my brass fitting to take solder properly after using this to scrub off the old oxidation. The retractable bristles are really handy, just like a mechanical pencil, so I can control how much comes out.