What is the cock used for?

If you are referring to the chock supplied with the truck (Mounted on top of the jack storage space), it is to be used to prevent the truck from rolling when you lift a tire.......Remember to observe correct safety procedures when jacking a Land Rover..... Put transmission in park with parking/hand brake ON hard!!!....or the car can/will ROLL when jacked because the park brake only applies to the transfer case output and via the centre diff which is unlocked (unless you locked it), the front axle could still roll unless chocked. a chock is a block of wood, brick, log, or a retail purchase that will stop a vehicle from rolling when you do not want it to. ie. jacking the vehicle off the ground. it can also be used if you must to work under a vehicle if all you have to work with is the jack. to be used only in a must situation. the right way is to chock the vehicle, jack it up, place it on jack stands and lower the vehicle onto the stands. the chock block should remain in place, unless you raise all four wheels off the ground then use jack stands on all wheels. Getting trapped under a vehicle is not a pretty thing. I have seen it, and it is ugly. hope it helps.