Offset gearboxes comprise two (or more) intermeshing flat gears, which effectively transfer power from the tool through the offset gearbox and directly to the fastener.

Though the open hexagon construction is by far Christie's most popular offset gearbox type, units are readily available with a variety of interface options including square or keyway designs for valve spindle actuation or allen key hexagon for confined cap screw work. Adaptors are often supplied to clients to reduce hexagon sizes to match multiple nut sizes.

The choice of driving force behind the offset gearbox is yours. Powerful pneumatic, electric or battery tools are ideal, even manual torque multipliers or torque wrenches can be used if speed is not an issue or if no power supply is available.