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.
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.