Here's one place to buy (with a picture)
http://columbiariverquilting.com/tow...ion_guage.html
Here's a video on using the TOWA:
http://www.youtube.com/watch?v=S7tzbj8_3fI
Penny gives a lot of credit to the Bobbin Genie, but I still use my TOWA on every bobbin, and I also use the Genie. I really, really hate frogging (rip-it rip-it)!!!