Here is a quiz - see if you can figure it out.
1. New Home style top tension (before Free aquired the name) Some do not have the lever part
2. Standard, again, many may be missing the lever. Note the rounded end.
3. National (and Eldredge) Foley & Williams is very similar.
4. New Royal (made by Free, but a quite different machine)
So far, I've not encountered anything that suggests Singer ever made a top tension machine, and until later models, Singer did not put names other than "Singer" on their machines.