Large Swedish bronze table clock

Hey folks!

I got this lovely large and super heavy (about 8,4 kg) Swedish table clock and a have a questions about the key. What is the purpose of the thinner part of the key? What it is used for on this clock?

Thank you so much in advance!


Kind regards,
Erik

 

I looked up the patent in the Swedish patent database:

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There's a link to a PDF description page if you can read the language. It's an image so it can't be plugged into Google Translate

This looks like a cross section view of the part Davey referred to. 11 in the diagram looks to me like it would accept that smaller key:

 

oops, I did a stupid

 

that looks rather post-war production. with the added & Söner (& sons) most probably towards the end of existence of the company.
https://www.radiomuseum.org/dsp_hersteller_detail.cfm?company_id=11267

 

Good eye. The patent looks to have been applied for in 1946, and granted in 1948.

 

afterwards they realized they don't come up with something elegant, so they switched to TV sets...