Carl Zeiss Jena Tessar 50/2.8 with 5-digit serial Nr.31191 dating and serial system question

Hello,

I have a Carl Zeiss Jena Tessar 50mm f/2.8.

Serial number: Nr. 31191 (5 digits).

This seems unusual to me, as it does not match the typical CZJ serial number ranges I have seen.

Is this a normal production serial number, or could it belong to a different system (such as a repair, reassembly, or special batch)?

Any information about its approximate production period or origin would be greatly appreciated.

Thank you.

Is this Leica thread?

mshchem said:

Is this Leica thread?

Click to expand...

It is M42 mount, not Leica thread.
I can also provide photos if helpful.

kedama said:

It is M42 mount, not Leica thread.
I can also provide photos if helpful.

Click to expand...

So then is this Contax???

mshchem said:

So then is this Contax???

Click to expand...

It is definitely M42 mount.
Here are clearer photos of the mount.

Does the mount construction look original to you?

I have no idea.