fred wrote:

But there's not much room for a groove in the edge. I'm looking at one
now where you have about 3/8" either side of the rope groove, so max
brush holder width could only be 1/8". Don't know why the rope has so
wide a groove, but it seems to be standard in those I've had dealings with.

All my sashes are 2" so there's plenty of room for machining but you can
use folded V-seals instead, I've used plastic but I think you can get copper
or brass ones too.
The ones I've used tend to flatten permanently under pressure