for fun - here are some tension types. This can be used as a clue to identify a machine, but keep in mind it's always possible someone swapped out a broken tension for one from a different machine. Some aren't interchangeble, and some look like they would be.
New Home
National - (Foley & Williams is similar)
Standard
New Royal
Florence
I was gonna take more pictures but you all got saved by dead batteries! I've got some real oddball looking ones on the less common machines. Don't have a Davis top tension though . . . another thing I may have to fix.