"Tim Watts" wrote in message
...
Does this actually mean what I think it means - the distance between the
vertical centres of the pipes as they come up from the floor into the
valves?

Because it seems an odd measurement and assumes all 90degree rad valves
have the same joint offset dimensions.

Or does it mean "distance between the two shoulders of the threaded ports
in the rad"?

It matters in a couple of cases

You can buy adjustable "tails" (that go between the radiator and the valve)
if it helps.