Locking a Yankee 133h

[B3nder]

I have a Yankee 133h which does not lock shut.

I've compared to the 131 and it appears that the lock nut is missing.
Did versions exist what had a notched type lock nut (similar to what I've got)
Of has it been removed/lost over the years?

It looks just like the 3rd and 5th picture on the eBay item 381882605356.

I have tried to lock it but to no luck, am I being a numpty?

 

[NazNomad]

I thought that knurled ring was the lock?

 

[B3nder]

It seems to be not as tool as other ones on the 131.

I can't lock it though, do the 133s even lock?

 

[Bod]

They don't lock closed.

Bod