Locknuts generally fall into two categories: prevailing torque (which resist movement immediately) and free-spinning (which only lock once tightened against a surface).
Prevailing Torque Nuts
These create friction even before they are fully tightened against a surface, requiring a wrench for the entire installation process.
- Nylon Insert Nuts (Nyloc): A popular and economical choice featuring a nylon ring that deforms around the bolt threads. They are effective for standard temperatures (up to approx. 120 deg C) but are generally considered one-time use as the nylon loses its grip once removed.
- All-Metal Locking Nuts (Philidas /Turret): Designed for high-heat environments where nylon would melt. The top of the nut is slightly pinched or crimped, distorting the threads to create a mechanical bind.
- Aerotight / BinX Nuts: These all-metal "stiff nuts" use a slotted, bent-beam design that acts like a spring to grip the bolt. They are often reusable because the metal returns to its original shape.
Free-Spinning Locknuts
These spin freely until they make contact with the bearing surface, making them faster to install by hand.
- Serrated Flange Nuts: Feature integrated "teeth" on the base that bite into the material surface. While effective, they can damage the finish or paint of the part being fastened.
- Thin Nuts: A traditional method where a thinner nut is "jammed" against a standard nut to lock the assembly.
- Castle or Slotted Nuts: These have slots that align with a hole in the bolt for a cotter pin. This provides a physical "positive lock" that cannot vibrate loose, commonly used on safety-critical parts like axles.
