The Shimano Deore BR-M6220 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 a new low-viscosity oil, updated piston seal, and 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 and control needed for long descents where the brake is working hard for extended periods. The temperature stability means the feel doesn't change between the top and the bottom of a long run."