As we all know, you don’t re-use nylon locking nuts….
The retaining nuts and bolts for the prop shafts on all Land Rover Series, Land Rover Defender & Land Rover Discovery 1 & 2 models are a 3/8 UNF thread. The original factory nylon locking nut thickness are a odd thickness. You can either purchase standard thickness retaining nylon locking nuts or thin nylon locking nuts. In most applications using the standard (but thicker than the original Land Rover nuts) will be fine.
On some applications such as on a Land Rover Discovery 2 front output prop shaft the bolt length are too short and the thin nylon locking nuts must be used. If you use the thicker nuts the thread on the bolt wont pick up on the nylon part of the nut enough to secure it.
The picture below explains it all. From left to right
Thin 3/8 UNF, Land Rover 3/8 UNF, Standard 3/8 UNF