Depending on the type of safety key you own, universal keys may also be available. Keep in mind that the safety key is there for a purpose. Do not attempt to bypass the switch or rebuild the treadmill around it. This raises the likelihood of bodily damage or fire. To prevent the line from pulling through the hole, insert a length of 3/16-inch diameter braided cord into the hole and tie an overhand knot. Trim the braided cord to around 36 inches in length. Connect the free end of the line to a plastic spring clip used to secure the cord to your clothing when working out on the treadmill.