The Shimano Deore BR-MT620 is a 4-piston hydraulic disc brake caliper built for consistent, full-power braking across a wide range of conditions. A dual diameter piston design delivers high power and precise control, and low-viscosity oil, an updated piston seal, and a heat-resistant resin piston keep brake feel stable across a wide range of temperatures. What Our Gearhead(R) Experts Are Saying:"Four pistons deliver the stopping power needed for long descents where the brake is under sustained load. The all-black finish suits builds where a clean, understated brake setup is part of the spec."