Typically adjustable shock absorbers just have an integral plastic knob or sometimes a screwdriver slot to adjust, the former shown below on left hand Spax coil over shock.
I wonder if you are referring to adjustable platform coil springs though also as below and which do require a C spanner?
![[Linked Image]](https://i.imgur.com/XYguLx8.jpg)
If you find one to accomodate collar diameter the lug of usual flat plate C spanner should fit it in adjusting hole as above. These ones have a hex grub screw to lock collar into place, others have two thin collars to lock adjustment against each other and require two C spanners.