GN 355.1 assembly tools serve to adjust GN 355 levelling elements. They are used in connection with a T-wrench or a hexagonal angle socket spanner. To ease levelling, the top end of the assembly tool has an external hexagon head which is used for turning the levelling screw with a ring spanner, ideally with a ratchet function. For adjustment, first use the assembly tool to turn the levelling screw of the levelling element into the desired position and at the same time tighten the screw to secure the levelling element. To ensure that the setting found does not change, the assembly tool may be used to counterhold.