Engineers with fastener manufacturers assure me if nuts and bolts are torqued to their proper value, they will hold within specifications without a lock washer. In fact, they warn lock washers can ...

The SR-71 Mach 3 spy plane is built of titanium, with titanium nuts and bolts. The sockets also have to be made from titanium, because the nickel in standard sockets corrodes the titanium bolts.