Isolation Feet with silicone 40°A or 60°A material. The harder 60°A feets are normally used on the heavier section. If you are purchasing these parts for DIY project and are not sure how to select, go with all 60°A feets or two sets of 40°A and 60°A each. The damping effect of NuPrime’s isolation feet absorbs and cancels vibrations that degrade audio performance. This manner of shielding from interference results in a pure and natural sound.