A compression fitting spanner is specially designed for tightening compression nuts as part of a compression fitting.
Regular spanners can be used for compression fittings, however, as their jaws are not designed to match a compression fitting nut they may not be as accurate and may slip on the nut in comparison to using a compression fitting spanner.
Compression fitting spanners can be single or double ended.
What is a compression fitting?
A compression fitting is a set of two compression nuts, a joint or union, and two compression rings (olives). It is used to connect two pieces of either copper or plastic piping together during plumbing work.