I am so excited to use these during mathematics.   I used Biggie Beads from a craft store.  To practice facts to 10 I used 10 beads on tongue depressors.  I was able to punch the holes with a hole puncher.  Next I made a set of Rekenreks for facts to 20.  I used paint stir sticks from Home Depot.  The wood was thicker than the tongue depressors, so I used a drill with a small bit.  The pipe cleaners went through easily.