The single ended compression fitting spanner has one spanner head to tighten or loosen 29mm (1.1″) compression nuts.
Double ended compression fitting spanners
The double ended compression fitting spanner has a different sized spanner head at each end to allow it more flexibility when working.
Which compression fitting spanner should I use?
The compression fitting spanner needed will depend on the size of the compression nuts you are using, although if you do a lot of plumbing work, the double ended compression fitting spanner will fit more nuts and therefore be used more often.