Brands like Teleflex, SeaStar Solutions, allpa, Solé & Johnson you can find them by allpa - Antal aluminum low friction rings & Dyna loops - Rings & loops - Antal deck fittings
Rope Shackle with Aluminium Low Friction Ring from 33,95 € | SVB
Low Friction Rings for Sailing - Practical Sailor
Low Friction Rings - Rutgerson Marin
Low Friction Rings
Low-friction Rings - Zero to Cruising
How to make a Brummel Lock Splice for low-friction rings - Yachting Monthly