here are some better pictures of the four I have. There may be more too.
These are the two that are different than the above. The first says "Singer No.66" on it -so no doubt what it is for LOL!!
Here are all four - the second to the right is missing the removable shirr plate, so that is not a "difference" between them.
And the back side
And some other items. The lower is a side clamp set, pretty sure it's for the 27. The upper is for the back clamp 66. The attachment foot is there for reference - the binder, hemmers and quilt guide are identical.
The differences are more evident from the back side.
This is a page from a manual showing this set. I'm after a cabinet with a molded drawer now too LOL!!
