It all started when I had to clean the shower. 'Surely,' I thought, 'someone else, who hates cleaning tile, has made a brush head for a drill.' Well, no one had. Or, at least, they figured it was so simple no one would need an instructable for it. So I made one without an instructable, and now I'm making an instructable for those who don't want to try it without instruction! So there you go. Super easy, super cheap, super fast. That's my kind of project!

Screw the machine screw almost all the way though the hole from the bristle side. Leave a few turns left to screw before threading the nut on. Tighten the nut with your fingers into the countersink around the hole. Then tighten the screw with the screw driver. If your brush doesn't have a countersink, don't worry about leaving a few turns before threading the nut, and just tighten the whole thing down.