Park pp 12 hydraulic brake piston press the unique shape and size of the pp 12 is perfect for compressing the hydraulic piston by pushing the brake pads apart to speed service and pad replacement updated shape to better fit 2011 and later shimano xtr callipers slide the polished wedge shaped tool between pads to expand the gap and pre set the pistons into the calliper useful if you have accidently pulled the brake lever without your wheel and brake disc in the bike reset the pistons without