This hole plug is specialized and designed for SUNLU FilaDryer S4. To prevent the moisture re-flow into the filament dryer. SUNLU FilaDryer S4 is a powerful filament dryer with the capacity of 4 spools of filaments and is compatible with all filaments.

If you are interested in Filament Dryer, Please back it: https://www.kickstarter.com/projects/sunluofficial/sunlu-filadryer-s4