The above picture shows the most common size of jaws: 1/2 and 3/4 inch.
Fixed basin wrench shaft
The fixed basin wrench’s shaft is a solid metal bar that connects the two jaw ends together.
1/2 inch jaws on a fixed basin wrench
The jaws of a fixed basin wrench protrude perpendicular to the shaft. This set-up allows the wrench to be rotated along its vertical axis and therefore be used in much more confined spaces than a traditional wrench or spanner.Although the jaws are referred to as being 1/2 inch, their actual internal width is 27mm. They are known as 1/2 inch BSP jaws because that is the size of the nut they are used on.
BSP = British Standard Pipe – A standard applied to thread size. So, a 1/2inch BSP nut will always fit a 1/2inch thread.
What does “rotating on the vertical axis” mean?
A fixed basin wrench is used differently to a traditional spanner because it rotates vertically, in line with the nut it is turning, as opposed to rotating about the horizontal axis like a traditional spanner or wrench. These wrenches will also work in the traditonal horizontal manner though few backnuts can be accessed from this angle.
3/4 inch jaws on a fixed basin wrench
The jaws at the other end of a fixed basin wrench also protrude perpendicular to the shaft (though they face the opposite direction). These jaws are known as 3/4 inch jaws as they are used on nuts with this standardised dimension. The actual internal width of these jaws is 32mm.