The NecksGen REV and Original units come with a fixed length tether that is a predetermined length to fit most drivers. Certain circumstances may require you to need a different length tether. Neck length, helmet drill locations, seating angles, shoulder muscle build, posture, and suit thickness may all play contributing factors into how much tether length/slack you will have. After installing your helmet hardware and test fitting your NecksGen in your car, have a friend help you do a slack test to ensure you are within the safe region of tether length for your situation.
Get buckled in your car as if you are ready to race and look straight ahead to the horizon. Have a helper lightly pull any slack from the tether all to one side. Pinch the tether to form a loop and measure the total length of the excess tether. This number should be 2.0 inches total (1 inch pinch). This is the ideal amount of slack. If it is not 2 inches, contact NecksGen for an appropriate length tether for your situation. If you have a REV, tethers are available in one inch increments. If you have a REV2 Lite, simply unscrew the pin that holds the tether to the device and insert it into the appropriate slot for you. Be careful when inserting the pin that it aligns with the back hole in the slot before tightening the screw, and do not overtighten.
For REV devices, the chart below shows the tether lengths that came pre-installed on your size device: