Thread Locking and Prevailing Torque: Choosing Between Loctite, Nyloc and All-Metal Nuts
A fastener that loosens on the line is rarely a torque problem — it is a locking-strategy problem. Specifying the wrong method adds cost where it is not needed and leaves the wrong joints unprotected. Here is how we deci
A fastener that loosens on the line is rarely a torque problem — it is a locking-strategy problem. Specifying the wrong method adds cost where it is not needed and leaves the wrong joints unprotected. Here is how we decide between liquid threadlocker, nylon-insert nuts and all-metal prevailing-torque nuts on real assemblies.
Match the method to the joint, not the catalogue
| Method | Best for | Watch-outs |
|---|---|---|
| Liquid threadlocker (anaerobic) | Threaded fasteners that must seal and lock, including setscrews | Needs cure time; wrong strength grade can seize service parts |
| Nylon-insert nut (Nyloc) | General vibration resistance, reusable a limited number of times | Loses locking after a few removals; temperature limited by the insert |
| All-metal prevailing-torque nut | High temperature, no polymer, aerospace/defence-adjacent use | Higher install torque; can gall on soft coatings |
| Mechanical locking (cotter, castle nut, lock washer) | Safety-critical, inspectable joints | More assembly steps and training |
The most common error is specifying Nyloc everywhere "because it is cheap", then watching it fail on a hot or high-cycle joint where the nylon has no margin.
Understand prevailing torque vs. clamp load
Prevailing torque is the resistance you feel before the fastener starts to clamp. A locking feature adds it deliberately. Two consequences buyers miss:
- A torque wrench set to 10 N·m may deliver far less clamp load if 4 N·m is spent overcoming the lock. Always specify the snug/target clamp torque including prevailing torque, not a generic chart value.
- Reused Nyloc nuts lose prevailing torque quickly. Define a maximum reuse count (often 3–5) and a quarantine for removed hardware.
For liquid threadlocker, the relevant number is the breakaway and prevailing torque after cure on the actual fastener and coating combination — not the bottle label.
Temperature and chemical exposure
Nylon inserts do not like sustained heat; above roughly 120 °C the locking function degrades. All-metal nuts keep working, at the cost of higher install torque and a greater chance of galling on plated threads. In environments with solvents, fuels or frequent washdown, the threadlocker chemistry matters more than the nut type — pick an anaerobic grade rated for the fluid, and confirm cure performance on your coating.
A short selection checklist
- What temperature does the joint see, sustained and peak?
- Is the fastener serviced in the field, and how many times?
- Does the thread need to seal (pressure/liquid) or only resist vibration?
- Is there a coating or plating that could gall under high prevailing torque?
- Can the line actually measure prevailing torque, or only final torque?
Answer those five and the choice usually narrows to one option.
FAQ: can I rely on a lock washer instead?
For light vibration, sometimes. For anything safety-relevant or high-cycle, a lock washer is the weakest of the options here and should not be the sole locking feature. Treat it as supplementary.
Wrapping up
Pick the locking method from the joint's temperature, service life and torque-measurement reality — not from habit. Define prevailing torque explicitly, cap reuse on polymer inserts, and verify the threadlocker against the actual coating. Those steps keep fasteners where they were installed.
For standard and custom fasteners with documented coatings and torque specifications, see Zimmor Hardware. Additional product categories are at zimmorhardware.com.
Originally published by Dev.to WebDev. Aggregated on AIWithGhost for educational purposes — full credit and traffic to the original publisher.