This silicone sock was specifically made for the Ring Heater. The silicone sock ensures that the Ring Heater keeps a stable temperature profile even when the part cooling fan is at 100%. Another advantage of the silicone sock is that it keeps the Ring Heater clean from any filament residue.
Which Version of the Silicone Sock do you need?
The Ring Heater V1 has an outside diameter of 18mm, so if you have this Ring Heater then you need the Silcone Sock V1. If you have the new Ring Heater V2 with an outside diameter of 14 mm then you need the Silicone Sock V2.