What is galling, and how is it different from rust?
Two surfaces slide against each other under pressure, bare metal meets bare metal and tears material from both faces, and if the surfaces are alike and soft enough to deform, the torn material fuses and the parts become one piece. Heat from fast turning makes it worse. A bolt rusted solid over years is a different problem: rust gives warning, and penetrating oil sometimes helps. Galling happens during installation, on new parts, often within the first few turns, and oil does not help, because there is no gap left for it to enter. In extreme cases galling leads to seizing, the threads freezing together, and continued tightening may break the part or tear off the threads.
Why are stainless threads so prone to it?
The chromium oxide layer that makes stainless resist rust also keeps the threads from touching bare metal to bare metal. Friction strips it off, and underneath, austenitic grades such as 304 and 316 are soft enough to tear rather than slide. Aluminium and titanium behave the same way: each has a self-forming protective oxide film, and once it is rubbed off the metals touch directly and begin to gall. As a rule, softer materials gall more and harder ones less; carbon steel galls to a lesser degree, partly because it is harder.
What makes it more likely?
Five conditions are named:
- Speed. Fast turning makes heat. Power drivers are the most common cause.
- Dirt. Grit, sand or metal chips in the threads act as an abrasive.
- Damaged threads. A burr, a dent, or a nut started at an angle.
- Identical materials. Two parts of the same grade and hardness gall far more readily than a mismatched pair.
- A tight fit. Threads at the close end of the tolerance range have less clearance and more contact area (Q1-07).
How do you prevent it?
A working sequence for stainless fasteners, which carries over to adjuster threads (Suncor Stainless sets one out):
- Inspect and clean the threads on both parts. Do not install a damaged thread.
- Put anti-seize on the male thread. This is the step people skip and the one that does the most work.
- Relieve the load on the link and back off both jam nuts before turning the body. Turning an adjuster under load or under jam-nut preload is the most common way a linkage thread galls (Q1-05).
- Start the thread by hand, several full turns before using a tool, and turn slowly all the way.
- Do not use an impact driver on stainless.
- Pair different alloys or hardnesses where the design allows. An austenitic stainless part mated with a duplex stainless nut galls far less, but when two different grades are used the nut must still be stronger than the bolt.
- Tighten the jam nuts to the specified torque with a wrench, not by feel.
One more point: lubricant changes the relationship between torque and clamping force. The same torque on a greased thread gives much more tension than on a dry one, so check whether the torque figure was set for dry or for lubricated threads. Using a dry figure on lubricated threads is an easy way to strip a thread. There is no general jam nut torque; use the value for the mating rod end and nut (Q1-05).
What do you do if a thread is already binding or seized?
- Stop turning. Every extra degree of rotation welds more of the surface together.
- Back it out slowly and steadily, not in short jerks. If it moves, keep going gently and remove it completely.
- Penetrating oil is worth a try, but expect little, since galling leaves no clearance for it.
- Controlled heat can break the bond on a bolt seized in a fixed part, through differential expansion, but only where the two parts expand differently and the surrounding materials and coatings can take it. A turnbuckle body and its ends are often the same metal, so it may do little there.
- If nothing works, cutting or drilling is what remains. Plan for that on any fastener you will need to remove later, and lubricate accordingly.
Can you reuse a galled part?
No. A galled thread is torn even if it came free and still looks usable. Torn threads no longer make full contact, so the joint will not develop the strength you expect, and the damaged surface will gall again immediately. Inspect the mating part too, since galling damages both.
Does thread quality matter?
Yes. The thread class decides how much clearance there is between mating parts, and tight threads leave less room for lubricant; rolled threads have a smoother, work-hardened surface than cut threads, which helps. Ask for the class when you order (Q1-07).
Is anything different for a tie-rod or suspension adjuster?
Yes: road grit and corrosion are the usual cause of a seized vehicle adjuster, and the awkward position tempts people into the wrong fixes. A pipe wrench or grips on a thin sleeve deform it and damage the thread. Heat near rubber boots, fuel lines, brake lines or tyres is a fire and damage risk, and it does little when the two parts are the same metal. Do not keep turning a binding steering or suspension adjuster: back it out gently, and if the thread is torn, replace the part, because a galled thread is not a safe load path (Q1-12). Prevention is the same as above: clean, anti-seize on the thread as the maker advises, the link unloaded and the jam nuts backed off before you turn the sleeve. The tie rod pages are the product pages.