How are Type-C Freewheel cogs secured to the body

I was noticing on my 11-34 type C Shimano freewheel a ring outboard of
the 11T sprocket. The ring has notches on the outside of the
sprocket-but none inside the diameter. Is this a snap ring or a lock
ring or a thin thread-on retaining nut?

Is the 11T a threadon typical of other Shimano smallest freewheel cogs
or is it splined like hyperglide cassettes?


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meb