This curious and blunt item, which is a well known knuckle-duster, was commonly used in trench war during WW1 during close combat to hit the enemy. But it was also a weapon used by concentration camp guards to punish the inmates and Polizei or Gestapo members to batter the captured enemies or persecuted people (Jews, communists, etc) so that they could get information from them. Some like this one have been found in concentration camp areas along Poland and Germany, mainly where the barracks of SS TK guards were located, and they were also available in period brochures of artifacts for Police and Gestapo. This knuckleduster is a ground dug example relict condition very rusty . We can guess the damage such a blunt item could cause in the person that was hit with it.