I just did a spool block exchange with some online and local friends. We used this :
http://annalenaland.com/?s=spool+block
block pattern. Its a free pattern, but I emailed and asked her anyway. She gave me permission and I gave everyone the link to print out their own pattern. Have them make a sample block before making all the blocks to swap. We all had a good time making them. I was disappointed that there were not more pieced thread sections, but they all looked cute pieced.