These are European Stitching Chisel made of SUS440C, which is one of the hardest stainless steels.
1. Make sure the tool is driven and pulled out in a vertical direction to leather.
2. Please work on a rubber pound board .
3. If the prong gets stuck deep in a rubber plate, make sure pull it out in a vertical direction. Do not shake or twist the handle from side to side, which will break the prong.