Thanks for all the replies.
The tachometer and speedometer are both equal, they both have an external shell.
The difference maybe be that the previous owner have changed them
(pretty unlikely, not easy to find parts here in Portugal and the bike was stored for the last 20 years, no ebay lol)
Or it maybe this is one of the last 20 XS1B, I think.
I tried to rotate the pin clock wise, but can only listen a click.
I thought it may detach in the area marked with the red circle.
No luck.
maybe i will cut it and re-attache with some mini threaded rod ...
it has 5mm (around 0.1968 inch), probably some M2 thread