The Prevailing Torque Principle

How Lock Nuts differ in their behaviour

A standard hex nut will thread onto a bolt until it comes to rest against the mating surface. At that time all resistance is from axial clamp force crushing the thread flanks together. Remove the clamp - via vibration, thermal cycling, or load reversal - and the thread friction lowers to almost zero. The nut backs down.
A Precision Hex Lock Nut addresses this failure mode by providing a friction element which is independent of the clamp load. The locking element, usually a nylon ring or a mechanically deformed segment of thread, locks onto the bolt thread by elastic or interference force. The nut resists rotation even in the temporary absence of clamp force. Engineers refer to this as the prevailing torque, or the torque needed to turn the nut through one complete revolution before it touches the bearing surface.
This is the main reason why a lock nut is preferable than a simple hex nut in dynamic situations. The locking feature is not a back-up feature, it is the primary anti-loosening feature and is engaged through-out the full threaded engagement.

Two kinds of locks: all-metal, nylon insert

The hex lock nut family has two different types for various uses. The choice should be based on temperature exposure, reusability, and regulatory constraints rather than familiarity with the type.

Nylon Insert Lock Nuts
Most common variation . A precisely machined nylon ring is assembled in the upper counterbore of the nut. The bolt is passing through nylon which elastically deforms over the crests of the thread; This results in constant torque and radial gripping force.

Lock Nuts – Metal Only
The top threads are mechanically deformed into an oval, rectangular or triangular shape to interfere with the bolt rather than a polymer insert. Because it has no non metal component, the nut locks at high temperatures when nylon would melt down.

Temperature ceiling: 120°C continuous (nylon will soften above).
Can be reused 2-3 times until the nylon ring loses its elasticity.
Non-corrosive nylon is compatible with most plating and passivation finishes.
Ideal for consumer assemblies, electronic enclosures and general vibration resistance.

Temperature ceiling depends on the base material (stainless 316 can take 800C plus).
Reusability: 5-10 cycles depending on the bolt grade and degree of deformation.
Ideal for engine compartments, exhausts, aviation and high temperature applications.

Both types are CNC machined. Our engineers evaluate the locking strategy during DFM assessment according to your operating temperature, cycle count and DIN 985 for nylon insert, DIN 980V for all-metal industry standard.

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Where CNC Precision Lock Nut Changes

The consistency of lock nuts is only as good as their geometry. A nylon ring counterbore must hold the insert at the proper depth and concentricity and an all-metal deformed thread section will provide constant torque over a production batch. These characteristics are achieved by CNC machining precision (like our socket head cap screws and self-clinching rivet nuts), not stamping tolerance.
Three-dimensional tolerances are essential for Precision Hex Lock Nut performance:

The thread pitch diameter shall be ±0.01 mm to ensure that the locking element bears at the correct depth on the flank of the bolt.

The nylon ring seat is concentric, so that the radial gripping is consistent, eccentricity gives a scattering in the torque of the nuts in the same batch.

Hex across-flats tolerance is +/- 0.05 mm so the nut seat is square and transfer torque without cam-out or rounding.

If tolerances are not the same, as is the case with stamped nuts of inferior grade, then the torque is unpredictable. In a batch one nut may grip at 2N.m and the next at 0.3N.m. In a vibration-critical assembly, inconsistency is inherent failure. KEY-CNC machines all nuts from solid bar stock on CNC turning centres and checks thread pitch and hex requirements before shipment.

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Besides Locking: Vibration Resistance

Precision lock nut specification is necessary but insufficient. Nuts are part of a threaded system, and bolt grade, thread class, surface quality, and grip length affect joint strength under dynamic load.
Three engineering principles regulate vibration-resistant assembly:

Grip length ratio: Increased bolt clamping thickness enhances joint flexibility, absorbing dynamic load without reducing preload. Lock nuts on short-grip bolts are far more fragile than those on long-grip bolts of the same diameter.

A zinc-plated bolt with a passivated stainless lock nut has a different friction coefficient than a bare-steel bolt with a black-oxide nut. The coupling is confirmed during DFM evaluation to keep torque within your window.

For thread class matching, a 6H nut with a 6g bolt offers clearance, while a 4g bolt creates interference. Lock nuts' thread class should suit the locking element.

KEY-CNC does not offer catalogue nuts for these reasons. Every Precision Hex Lock Nut is made to your drawing with thread class, material grade, locking type, and surface treatment for your assembly environment.

Material Selection and Surface Treatment

The table below maps common material-locking-finish combinations to typical applications. All finishes are RoHS-compliant and applied in-house as part of our one-stop metal processing capability.

Base Material	Locking Type	Recommended Finish	Typical Application
Carbon steel 45#	Nylon insert	Zinc plating / Black oxide	Industrial machinery, frames
Stainless 304 / 316	Nylon insert	Passivation	Medical, food-grade, outdoor equipment
Stainless 316	All-metal	Passivation / Electropolishing	Marine, high-temperature environments
Aluminum 6061-T6	Nylon insert	Anodizing	Weight-sensitive assemblies, robotics
Brass C360	Nylon insert	Polishing / Nickel plating	Decorative hardware, electrical contacts

Drawing to Delivery

Within 24 hours, our English-speaking engineers check STEP, IGES, or DWG files for thread size (metric M3–M20 or imperial UNC/UNF), locking method, material quality, and torque aim. North America and Europe prototypes 7–10 days, and volume manufacture 2–3 weeks.
Our hardware insertion services and fastener production lines follow ISO 9001:2015, therefore every batch ships with material certificates and inspection reports. With 16+ years of precision production experience, 1,000+ collaborating clients, and 95%+ customer repeat rate, OEM teams select KEY-CNC when a standard hex nut is not enough.
Ask our engineers for a custom Precision Hex Lock Nut for vibration, heat cycling, or regulatory compliance in your next assembly.

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