This article contains replacement O-rings and nylon inserts for the Alphacool Eiszapfen Pro fittings. The wide O-ring is inserted inside the Eiszapfen Pro fitting and seals the HardTube. The nylon inserts are only required for PETG HardTubes. PETG HardTubes are soft compared to acrylic HardTubes and can deform from rising temperatures and compression forces. This happens especially at the outlets of GPU and CPU where they reach higher temperatures which can contribute to the deformation of PETG HardTubes. These deformations can lead to leakage. The nylon inserts prevent this deformation in combination with the Eiszapfen Pro connectors.Please Note: Not recomended for use with Bitspower brand tubing.