I do have a set (never used) of the square-cutout B7 brushes. Besides not wanting to use them and ruin them, I figured they would not work as well as separate steel-wool pads since only part of the brush surface would be covered with the steel wool.
I just learned from Tom Gasko -- and now you! -- that there was also a PN brush roller with horsehair bristles. I never knew that. Nor did I know about the other variables.
I don't think the 3-brush roller was standard on the CB. Possibly the CA, but I remember a brand-new CB (chrome & 1205-turquoise) in a church where I used to play the organ. It did have a long coiled-vinyl hose (light gray) with a 3-wire PN cord strapped around it. But the PN had a standard brush roll; I clearly remember that. If it had been anything but a standard brush roll, I would have noticed!
