A basin wrench serves the same function as a normal wrench but is designed to be used
in places that a normal wrench could not be. It consists of a long handle with a head at
one end that can be tilted in one plane up to 90 degrees. The purpose of this is so that the
head may lie in the horizontal plane while the handle is held vertically. The head consists
of two metal jaws (like a pair of pliers) connected by a spring-loaded hinge, so that it may
grip things of various sizes. At the other end of the handle, in my particular model, a bar
may be added perpendicular to the handle (by putting it through the hole in the handle)
for increased leverage in turning the wrench.
I believe it is called a basin wrench because it is specifically designed for manipulating
the fasteners that connect the lines that lead from the water cutoff valves below the
bathroom sink to the underside of the faucet. The problem is that the faucet is much
higher than the basin of the sink, so the nuts that attach the hoses to the faucet are in a
very narrow region between the underside of the basin and the wall (about a 4" wide
space in my case); thus, no normal wrench can be used because the handle must be in the
horizontal plane, where there is no space. Although the fasteners are hex locknuts, a
socket wrench cannot be used because the hose immerges from the middle of the nut, so
there's no way to put the socket on. What one needs is a normal wrench with a head that
is turned at right angles to the handle, which is exactly what the basin wrench is.
Mainly, I was amused by the label on the package reading, "Spring-loaded jaw securely
grips any nut."