Most modern domestic machine needles have a flat shank. The flat can go on the right, left or even the back side. The 66 has the flat on the right and the 221 has it on the left.
There are many sites that have information about the different needle systems. This link is basically for early needles and has a link for a pdf that is searchable.
http://ismacs.net/needle_and_shank/i...edle-list.html and they also link to
http://ismacs.net/needle_and_shank/i...edle-list.html
Here is a link that tells about "some" of the presser feet shanks
http://ismacs.net/needle_and_shank/shank.html
There are other sites on the web that tell the difference between low, high and slant shank feet. The top clamp feet is a whole 'nuther ball of wax.' The really early machines were different still.
Janey - Neat people never make the exciting discoveries I do.
Not affiliated with off-site link(s)