the pivot-point of the hammer, depending on the particular firearm under discussion. When the tumbler/hammer rotated quickly from full-cock, the spring-loaded metal plate could not engage into the slot cut into the tumbler, and the firearm could fire since the hammer would fully rotate. When the tumbler/hammer rotated slowly from full-cock, such as when engaging the half-cock notch, the metal plate would slide into the slot cut in the tumbler, thereby preventing the hammer/tumbler from rotating fully, hence preventing the hammer from falling and the gun from firing. In practice, the half-cock notch was often prone to breakage when used as an early safety mechanism, whereby the tumbler would have part of the metal around the slot shear away, thereby removing the fragile safety mechanism, and permitting the hammer to fall and the firearm to fire. This could occur from accidentally dropping the loaded firearm onto its half-cocked hammer even once. References Firearm terminology