I use my disc sander for all sorts of tasks in my shop. Because of this, I end up changing the discs quite often. To help me remember which grit disc is currently on the machine, I came up with the simple solution you see here. Since I store my extra sanding discs in a wood storage “tower”, I was able to drill a series of holes down the side and install hooks in each position. I then wrote the grit numbers on metal-rimmed key tags.
When I pull out a disc to put on my sander, I remove the same key tag from the hook on the storage tower and place it on a magnetic hook that I leave on the disc sander. This way, I always know which grit disc is on the sander.