The way Nordlocks do not work is where there is relaxation under the screw head. They will not work on wood, soft plastics etc. They would be iffy with a wood prop, but under the CF Mej props or aluminum standoffs and the like, they are are a 100% solution. For engine mounts, I embed brass tubes through the firewall so that the compression forces under the screws do not compress the plywood firewall. BTW, I still remember a Prof in school that drove home the point that a screw is a screw is a screw, until you put a nut on it, then it becomes a bolt.