Devil's fist (=Pirunnyrkki in finnish) is a finnish traditional puzzle usually made from wood. Its a 6 piece puzzle where the object is to complete it like shown in the picture.

Puzzle itself is not the hardest, but it can take some time to figure out. Maybe that is the reason why its called that way: you get frustrated and wave your fist in the air cursing the devil. Who knows?

Have fun!