Editing Disc brake (section)

===Adjustment mechanism===
In automotive applications, the piston seal has a square cross-section, also known as a square-cut seal.

As the piston moves in and out, the seal drags and stretches on the piston, causing the seal to twist. The seal distorts approximately 1/10 of a millimeter. The piston is allowed to move out freely, but the slight amount of drag caused by the seal stops the piston from fully retracting to its previous position when the brakes are released, and so takes up the slack caused by the wear of the brake pads, eliminating the need for return springs.<ref>{{cite book|first1=Mike |last1=Mavrigian |first2=Larry |last2=Carley |year=1998 |title=Brake Systems: OEM & Racing Brake Technology |page=81 |publisher=HP Books |isbn=978-1-55788-281-3 }}</ref><ref>{{cite book|first=Fred |last=Puhn |year=1987 |title=Brake Handbook |page=31 |publisher=HP Trade |isbn=978-0-89586-232-7 }}</ref>

In some rear disc calipers, the parking brake activates a mechanism inside the caliper that performs some of the same functions.