I was told by a Stateside Brit, if worst comes to worst solder a bolt to the disc. Then double nut the bolt and use a box end wrench on the bottom nut. I apologize if my American English is unclear. I do know about pins and turnscrews. Don't know if a box end wrench is a spanner. In my limited work I've seen significantly more problems with disc set strikers than hammers with integral firing pins.