Around three years ago Doc Hammett, of Totally Stainless, called STREET RODDER Editor Brian Brennan because of a recommendation in a tech article not to reuse Nylock nuts. Doc had remembered a tech release by the Nylock corporation that stated their nylon insert lock nuts can be reused over 100 times (because nylon has memory it will gradually return to its original shape when deformed). Since Totally Stainless stocks a full range of nylon insert lock nuts and had destroyed a common myth, Brian suggested Doc write an article about locking fasteners and address pros and cons of their uses and, better late than never, here it is. -Senior Editor Ron Ceridono
Safety wire is an effective...
Safety wire is an effective means of locking fasteners when installed correctly. Note how one bolt trying to come loose will tighten the other.
Did you ever notice that highly stressed fasteners like rod, main, and head bolts don't use any locking devices? These critical fasteners stay tight by being stretched-they work like clamps. If a fastener can't be stretched enough to create adequate clamping force, then a locking device may be needed. But it's not always practical or even desirable to use a properly torqued high strength bolt for many automotive applications, such as fenders or hood hinges, but there are other means of securing fasteners.
There are a wide variety of locking bolts, nuts, and washers on the market. These can be divided into three types: externally applied devices, prevailing torque, and free spinning.
Externally applied devices include safety wire, locking tabs, pins, and clips. These are often used on critical components (like suspensions) because it is easy to verify that the fastener is locked into place. These devices provide very positive locking but may be difficult to install and remove. Safety wire can be a real pain but it does have that nostalgic racer look! These devices need either a stationary object to work against or another fastener to be paired with.
Lock washers also come in...
Lock washers also come in a variety of forms-split washers come in standard and high collar diameters (left middle and upper), toothed washers (middle) can have internal or external teeth and some are available for countersunk holes, and wave washers and Belleville washers are often found in light-duty applications (right). The unique wedge lock washers are relatively new and extremely effective (lower left).
Slotted nuts (often referred to as castle nuts) and cotter keys are used on many suspension parts; we are often asked if we stock them. We don't because standard industrial stainless castle nuts should not be used on suspensions because they have yield strength of only half of what is used originally. Castle nuts have prongs that are smaller than the full hex of the nut; slotted tall nuts are normally used on automotive suspensions. We can make the proper strength slotted nuts from high-strength stainless stock-but the height of the nuts and the location of the slots do not follow any fastener standard. Slotted nuts are provided with the part when purchased and the nut height is determined by where the hole is located in the threaded shaft of the part!
Prevailing torque fasteners use a thread interference type lock where there is resistance to removal even when the fastener isn't fully seated. Automakers often use these type of lock nuts on suspension parts to provide extra security for critical parts that may loosen due to long-term wear or other factors. Nylock nuts are one of the most familiar of this type. Caution must be used when using prevailing torque type fasteners in stainless. Stainless has a tendency to gall-the surface of the threads can tear and lock permanently to the mating surface. The friction produced by prevailing torque locking features increase galling problems. Appling a liberal coating of antiseize prevents galling under most conditions.