Originally Posted by Miz Johnny

Your Singer 66 is a low shank straight stitch machine. The feet used on it depends on the sub-model. 66-1 was a back clamping machine, and will only take back clamping feet. The rest will take any low shank Singer SS feet, often found in those green cardboard boxes with Singer on the top.

There's quite a bit of information here:

http://www.ismacs.net/singer_sewing_...cessories.html

Some pictures of back clampers here:

http://www.worthpoint.com/worthopedi...ne-attachments

I'm sure there are better links out there, but these are some quick ones to get you started.