Evans Hydraulic Glass Rock Drum Head Tom Pack. Hydraulics feature 2 plies that sandwich a thin layer of oil to give the fat, wet sound that was pioneered in the '70s. The oil decreases sustain and enhances attack without effecting feel. These heads produce a big fat wet sound! Product SpecificationsEvans Hydraulic Glass Rock Drum Head Tom Pack Specifications Drumhead Sizes: 10, 12 and 16 inch Drumhead Types: Hydraulic Glass Fusion