Next up in the ICS Class for ICS Airsoft AEG owners, as well as general AEG owners, is about the Gearbox Spacer. There are other spacers for the gearbox but when you here about shims, then it is about this to ensure that your gear does not wobble and aligned precisely. When your gearbox gears start to wobble, then it is high time you replace the shims/spacers.