This patented contour lock system allows the Contour Battery Master Switch to be used as individual units or locked together with other switches. The featured control knob is non-removable while in the ON/OFF position. You can remove the control knob by rotating the knob to an anti-clockwise 45 degree position. All sides are removable for access of up to 1/0 cables as well as a rear cover insulating the back terminals from short circuits.