Product DescriptionHydraulics feature two plies that sandwich a thin layer of oil and give the fat, deep, and short sound pioneered by early 70's rock and roll. The oil decreases sustain and enhances attack and low-end. Additionally, Hydraulics are famously easy to tune...making them a perfect fix for troublesome drums and younger players looking for instant sound.From the Manufacturer Hydraulic Glass Series Overview Evans clear Hydraulic series features a thin film of oil between two plies of thin film offering maximum durability, a fat, deep and short sound pioneered by early 70's rock and roll. Hydraulics are famously easy to tune, making them a perfect fix for troublesome drums and players with little tuning experience. The revolutionary Evans Level 360 drum head technology is found in the proprietary collar design that extends the level playing surface of the drum head 360 degrees around the drum. This vertically enhanced collar design ensures balanced contact with the critical bearing edge of the drum shell, resulting in: ? Ease of fit ? Ease of tuning ? Extended tuning range and quality of sound Available on all Evans 6 - 20 inch Batter and Resonant Drum set, Snare Side, Concert and Marching Tenor heads. Evans Level 360 technology solves the age-old dilemma of traditional synthetic heads consistently not fitting a variety of drum shells without using force that chokes the responsiveness of the head and the drum?s performance. The Level 360 Blueprint The benefits provided by Evans Level 360 technology stem from a groundbreaking collar design: Steeper Collar:Extends the level plane of the drum head to ensure balanced contact with the critical bearing edge of the drum shell. Roll-over Hoop:Provides strength and stability where the film meets the hoop, for greater durability without diminishing performance.Balanced Contact:For ease of tuning and enhanced quality of sound. Greater Tonal Range:Wider tuning options result in higher levels of responsivness and resonance, giving you the confidence to tune your drums high or low.