Interesting item... A lot of people digging for relics don't know about Soviet grenades. They have a number on them for delay, including a zero grenade. It was built to use as a bobby trap, NOT to be thrown! So if you find an old Soviet type grenade - don't pull the pin. There is a Youtube video of some fishermen using grenades that don't know this.
https://www.youtube.com/watch?v=WwsZq7_LN9I