This grenade is post-ww2, but used the M41 stickgrenade , converted with the use of a plastic adapter to replace the wooden stick. It has the "Syt55" fuze mechanism.
Thanks Francesco for this information.

Photo on the right © B. Bosman.

On the right and below are some photos of the SYT55 fuze.
Apparently this fuze also found use on Russian F1 grenades, which were re-threaded to make this fuze fit.
I don't know the Finnish name for this variation.

Photos © Dr. Ruby.

SYT55 compared to a WW2 UZRGM :