Why mess with winding line. This refill cartridge of pre-wound spool is a simple and convenient solution for your RYOBI cordless trimmer. Just pop the new pre-wound spool in your RYOBI trimmer and you're ready to get back work. This quick, easy solution is ideal for all RYOBI auto-feed cordless trimmers- 18-Volt, 24-Volt and 40-Volt.