Screwdrivers, nut drivers, and keys are used to tighten and loosen fasteners. Screwdrivers are for turning screws while nut drivers are used on nuts and bolts. Hex keys are used to turn bolts and screws with an hexagonal-shaped indentation in the fastener head. Torx keys are used to turn screws and bolts with a six-point star-shaped indentation. Service keys are used to turn fittings and fasteners and are compatible with one type of product or brand to limit tampering.