Optional Machined Adjustable Motor Mount for the Traxxas X Maxx YOU WILL RECEIVE:- Two piece Adjustable Motor Mount with replaceable lock nut- Lock nuts are to secure fasteners or shaft with threads- A lock nut comes with a nylon insert that conforms to the threads of the screw- The nylon insert grip against the threads that reduces the chances of loosening due to the vibration- For best performance use new lock nut.