Fan Worms--How big will they get?

I was doing a water change today and decided to actually clean the glass. Lo and behold I seem to have a whole bunch of these cute little red fan worms. Amazing what you can see if you clean the glass off! I was wondering how big these guys will get. Right now they are about 2-3 mm wide. pretty small. I don't think my camera can get a decent shot or I would post pics.

I'm not sure how big they get but wanted to say how nice it is to see a post from you! Can you come to the Feb 16th meeting by chance?

Now, back on topic.

I've seen them hit around a half inch. Tops, usually.