Can differentiate with double digits (double digit by double digit multiplication or even fractions). This site has great math projects. This can be done with nails in a board and colored yarn. Makes a great pricture too.
I originally saw this idea on Offbeat Home a while back. I wasn't able to find any specific tutorials on how to make the threaded house numbers online, so I figured it out as I went along. Here's how you can make your own industrial house numbers.