Low friction KRO open rings. The passage is optimized to pass the line with light force and to prevent it from exiting during use.
This open ring allows the furling line to be perfectly aligned in the drum furler and the rope to run perfectly along the stanchions. The furlers are by definition flying and open rings make it very easy to install and remove the furling line.
The KRO was originally designed for the furling line but it is ultimately used for many other applications: barber haulers, reefs, lazzy jacks, etc.