From Team 449 Wiki
A wrench is an important tool mainly used to tighten and loosen nuts and bolts. There are a variety of wrench types, but the ones used most frequently in robotics are the adjustable, combination, hex key, and T-wrench.
An adjustable wrench gets its name from its ability to change sizes. This allows one wrench to loosen a variety of different bolts and nuts. The range of the wrench varies depending on the size of the wrench.
A combination wrench has two ends that can be used to tighten and loosen nuts and bolts. One end is open while the other end is a box wrench, meaning that it is closed. Both ends are typically the same size and cannot be adjusted.
A ratchet wrench like a combination wrench has two ends that are not adjustable. One end is an open wrench while the other is a [ratchet].
Hex Key or Allen Wrench
A hex key, also commonly referred to as an Allen wrench is used only for tightening and loosening hex-head screws and bolts. They are small and L-shaped and come in a variety of diameters and lengths. They may come separately or as a set containing different sized wrenches.
T-Wrenches are very similar to hex keys in that they are used only for tightening and loosening hex-head screws and bolts. Their name comes from their shape. T-wrenches have a very long hex shaped shaft attached to handle, creating a T shape.
Safety and Other Tips
Righty-tighty, lefty-loosey! Use a ratchet as opposed to a standard wrench when you have limited mobility.