Originally Posted by QuiltnCowgirl
Here's the 1949 Singer blackside 128-23 I picked up Saturday.
The attachments you asked about are "top clamp" and go to one of these:
Davis, New Home, Standard, White, Domestic, Kenmore, Free-Westinghouse, or National.
(list from the book by Charlene Phillips, The Sewing Machine Attachment Handbook)
Evidently there are 12 different sizes of these top clamp attachments that all fit different machines...