: Distinguished by its "X" or plus-shaped tip, it is designed for Phillips screws. This design is self-centering, which prevents the driver from wobbling and reduces the risk of slipping sideways compared to slotted screws. Contextual Usage in Maintenance

In the world of mechanical assembly and maintenance, these two screwdriver types remain the most fundamental:

The phrase appears to be a direct instruction or requirement from a technical manual or assembly guide, likely for an Instron testing system. In such contexts, "121" often refers to a specific procedure or page, such as testing limit stops or general maintenance, where these two tools are the only ones required. The Two Essential Driving Tools