most common fasteners used in mechanical assemblies are bolts, nuts and screws. Bolts usually (but not always) have hexagonal heads, as do nuts. Screws usually (again, but not always) have round heads and a slot or other recess to accommodate the appro- priate driver tool. Nuts and bolts are most often tightened and loosened using wrenches, sockets and nut drivers; likewise, screws are driven tight or loosened using screwdrivers. There are myriad varieties of these tools and each have uses at which they excel. Let's explore these tools and what they're used for now.