Punch cut sorbo pad designed to help prolong gearbox life whilst also helping to correct AOE on higher ROF / FPS AEG's. Also, a Sorbo Pad cushions the Cylinder Head from the Piston Head, helping to make your gun run quieter. Lots of good guides on YouTube.
Correcting AOE isn't essential but can help performance in certain situation.
These pads are punch cut so the centre hole isn't always 100% centered, some may be 1mm or 2mm off. This doesn't affect the way it works.
Overall Diameter: 20mm
Center Diameter: 7mm