Six Degrees of Freedom - In engineering terms, refers to the ability to move three-dimensionally in space about the Cartesian coordinate system of X,Y and Z, including rotation about each axis. That is to say, an object can translate in all 3 planes, XY, YZ and XZ including rotation about the X,Y and Z axes. 6D's mission is to provide the public with superior safety helmets from both a technological perspective and a design perspective. They continually challenge the company to improve its technology and lead the marketplace with innovative designs. Available in five sizes from 35 mm to 55 mm, ATR-1 Super-Cool cheek pads provide the perfect tool to create your personal custom fit. Also, it's great to have an extra set to switch-out between races. Snaps in-and-out in seconds for fast and easy attachment and removal. The Emergency Release System provides easier access and helmet removal during emergency situations.