nylon nut in place of castellated nut

They're often called nylock nuts. They work fine in most applications, but you can only take them off a few times before the bolt threads wear a groove in the nylon, and they loose some of their holding power. When new they hold well, and are obviously easier to use than the castle/cotter pin setup. I've been given nylocks as replacements for castellated nuts in suspension kits, in places where the whole car and occupants would be at risk if something failed. In a situation like that, there's no way I'd reuse a nylock nut; I'd replace it (being careful to get the same grade) every time I had it off.

Cheers, Walt

Late model auto suspension, especially some orientals, is very often done with "crushed thread" nuts. These are better than nylocks, but are strictly one-use things. Their interior diameter is ever so slighly 'oval' in shape. I used them with great success on an old Harley with its original

1940-something springer - something that I could never afford to have come loose. And it never did. It's been on the road for twenty years that way. (Crushed threads do not harm the bolt thread at all.) You can get them in most any size, metric or American.