Typically, the roller needs to be a little bit wider than the width of the composite band that is being laid down. So for four tows the band width (as compacted) is usually around 1.06 inches wide. The roller is roughly 1.37 inches wide. It probably could be a little narrower. If the tapes move a bit on the roller you don’t want them to fall off of the edge of the roller!
So if you are running two tapes, you could, in theory, make the roller narrower as well. However, remember that at this time, if you are running two tapes, they need to be in tow positions 1 and 2 on the head. That means they will be offset to one side of the centerline of the head. The roller would need to match that.
The rollers typically have a metal core, usually aluminum, and an elastomer is molded around the core. The elastomer is typically a urethane, but from some clients we have used silicone as well.