In article ,
says...
I want to tighten a chrome plated hexagonal nut on a central heating radiator
valve without marking it in anyway.
(Part of a so called designer fitting.)

Any suggestions as to the best ways of doing this? I was considering getting a
spanner of the right size and if possible using some thin paper between the
spanner and the fitting.

Use a spanner a millimetre oversize and wrap a bit of Fairy Liquid
bottle around the nut. Or wrap a bit of old leather belt around the nut
and use Mole grips or a Stilson wrench.