OK so it's the same set up as those I have. Wasn't sure so I was keeping mum.
Here's some more pics to go with the one SteveH posted.
[ATTACH=CONFIG]471749[/ATTACH]
This is for the White DRESSMASTER. Looks to be almost identical to the White FR.
[ATTACH=CONFIG]471750[/ATTACH]
This is my Kenmore 117-720, a White made rotary. With the exception of the top thread guide the threading is the same as the FR.
[ATTACH=CONFIG]471751[/ATTACH]
A close up of the check spring.
Joe