Almost all screwdriving applications can be ascribed to two basic forms – hard screwdriving applications and soft screwdriving applications.
Hard screwdriving applications are all applications in which there is a hard material (usually metal) directly under the screw.
Soft screwdriving applications are all applications in which there is a yielding (soft) material (usually wood) directly under the screw or it is being screwed into a yielding material.