We use a "stover" nut
https://en.wikipedia.org/wiki/Distorted_thread_locknut
A Nylock will not work as the heat melts the nylon and split lock washers fail with the heat cycling (takes the temper out of the steel) and allow the nut to loosen with the vibration. As this is a "tension" rather than "shear" application, a grade 5 or better will work although some bolts handle the heat cycling better than others.