There are two very different approaches to installing fasteners on a job site. In one case, the impact driver was run until the screw stopped turning, and then it was run for another half-second. Another guy tightens it until it “feels right” and moves on.
“The one is over-tightening. The other is under-tightening. They’re both wrong. And they both can cause failures weeks, months or years down the road — when the customer calls and asks why their deck is loose, their roof is leaking, or their equipment is rattling.
The problem is that most contractors and installers rely on their “feel” for torque, but that’s not an accurate approach. Torque is a clearly defined, measurable engineering parameter. If you handle it improperly, you’ll create a potential failure point in every fastener you tighten.
This article explains what torque really is and what can go wrong when you have too much or too little, how to find the appropriate torque setting for your fasteners, and what you need to know for installing each type of screw.
What Torque Actually Does – And Why It Matters.
During installation, torque is applied to fasteners to rotate them. The clamp force is what holds two materials together and keeps them together.
Think of it this way: the torque is what you turn. The clamp force is what holds.
The fastener stretches slightly when you tighten a screw. Tension is created by that stretch. As a result of that tension, the joint is pulled together. Vibration, movement, and separation are less likely to occur when the clamp force is stronger.
Why torque is important: A fastener that isn’t tightened enough will loosen when subjected to vibration. A fastener that’s over-tightened can be stretched past its yield point, weakened and fail—sometimes catastrophically. Good torque will ensure that the fastener achieves its design clamp load, and that the fastener, or the material, doesn’t get overstressed.
In other words, the torque must be high enough to create sufficient clamp force, but low enough to avoid damaging the fastener or substrate. The range is narrower than most people realize.
Over-Tightening and Under-Tightening – What Actually Happens.
Over-Tightening: The Damage Is Often Invisible
Over-tightening means you’re putting more torque on the fastener than the fastener or the material can handle. The results are different depending on what you are fastening.
Wood: Excessive torque crushes wood fibres, strips threads, or cracks cladding. In timber screws, over-torque is one of the main causes of premature failure under dry conditions. Excessive torque during installation undermines the strength of the screw. Over-tightening lag screws can also cause joints to no longer perform at their true strength.
Thin metal: Over-torque tears through thin sheet metal, strips the hole, or snaps the screw head. Once the hole is stripped, replacing the screw does not solve the problem; the hole is already damaged.
Concrete: Over-torquing a concrete screw can strip the threads it has cut into the hole wall. The screw spins but does not tighten. The connection is compromised.
Sealing washers: If a screw with a sealing washer is tightened too much, the washer bulges out and the inner lip seal (EPDM) can be damaged. The washer looks fine but no longer seals.
Catastrophic failures: Over-tightening has caused real structural failures. An investigation into a bridge deck collapse found that the principal cause was accidental over-tightening of bolts using an impact wrench, which damaged the threads. A few extra ugga-duggas with an impact wrench can bring down real structures.
The problem with overtightening is that it usually looks fine right after it’s installed. The fastener is countersunk. The joint is tight. The damage is not seen until the connection is under load.
Under-Tightening: Slow, Steady, and Inevitable
Under-tightening is less dramatic than over-tightening. No snap, no crack. Just a fastener that slowly, quietly loosens over time.
Vibration loosening: A fastener not tightened to the correct torque lacks sufficient clamp force to resist loosening. Vibration from wind, traffic, or machinery gradually rotates the fastener out of the joint. Under-torqued bolts loosen from vibration.
Leaks: An under-tightened sealing washer does not compress. There is too much slack in the fastener, so tightness cannot be guaranteed. Rain finds its way in. Rust follows.
Structural failure: Under-torqued structural bolts can lead to building failures. The connection is weaker than the design assumes. As time goes on, the joint moves, the load transfers to other fasteners, and ultimately something fails.
Equal probability: Over-tightening and under-tightening are caused mainly by inaccurate assembling and have equal probabilities. Both are equally common. Neither is acceptable.
How to Find the Right Torque – References and Real-World Practice
Torque is not guesswork. It is determined by several factors: fastener diameter, strength grade, thread type, and lubrication condition.
General Reference Values
The values below are general references for dry (unlubricated) fasteners. Always check the manufacturer’s specification for your specific fastener and application.
| Fastener Size | Grade/Class | Recommended Torque (Dry, N·m) | Notes |
| M6 | 8.8 | 9–12 | Common in light machinery and furniture |
| M8 | 8.8 | 22–28 | Standard structural and equipment fastening |
| M10 | 8.8 | 46–55 | Heavy equipment and structural connections |
| M12 | 8.8 | 80–95 | High-load structural applications |
| 1/4″ | Grade 5 | 11–14 (lbf·ft) | General construction and equipment |
| 5/16″ | Grade 5 | 21–26 (lbf·ft) | Structural and heavy timber |
| 3/8″ | Grade 5 | 38–46 (lbf·ft) | Heavy-duty structural connections |
Important notes:
Lubrication reduces torque requirements. A lubricated fastener requires 20-30% less torque to achieve the same clamp force.
Stainless steel fasteners have different friction characteristics. Lubrication is often required for stainless steel; this reduces torque values.
Use the manufacturer’s specification if available. The values above are general references. Specific products may have different requirements.
Real-World Installation Method
Step 1: Tighten it snugly first. Drive the fastener until it just touches the surface. Apply no force, just make contact.
Step 2: Torque to specification.Trabaje conuncalibrador de torque. Ajuste el valor recomendado. Torque suavemente – no jale la llave, Esto podría hacer que pase por alto el valor preestablecido.
Step 3: Check the sequence.Assemblies with multiple fasteners should be clamped in multiple passes in a star or crisscross pattern. As a result, clamping force is distributed evenly.
The tool that matters: A torque wrench is the tool you use to drive a fastener to a specific torque. In construction, Undertorqued structural bolts can cause building failures; overtorqued bolts can crack concrete.
What not to do: Don’t final torque fasteners using a rattle gun (impact wrench). Tighten to the specified torque: Any fastener required to be tightened to a specified torque should be applied to that torque using a properly calibrated manual torque wrench. Impact wrenches are for rough installation. For precision, use Torque Wrenches.
Torque Characteristics by Screw Type – What Each One Needs.
Different screw types have different torque behaviours during installation. Understanding these differences helps you avoid the most common failures.
Self Drilling Screws
Torque behaviour: Self drilling screws have two distinct torque phases. The first is the drilling phase—the drill point cuts through the material. The second is the seating phase—when the head contacts the surface, torque spikes sharply.
What to watch: The torque spike at seating is where most failures happen. If your clutch is set too high, that spike will strip the hole, crack the material, or snap the screw head.
Best practice: Use a clutch-controlled screwgun, not an impact driver. Set the clutch low and increase gradually until the screw seats without damaging the material. For standard speed and torque reference values, see our detailed installation parameter guide.
Self Tapping Screws
Torque behaviour: Self-tapping screws cut their own thread while being driven. Installation torque increases progressively. No sudden spike, but a gradual increase as the threads engage.
What to watch: With thin materials (under 1.0mm) self-tapping screws can strip the hole if the torque is too high. The threads bite into the material but if there is not enough thickness of material to actually grab the threads completely the hole strips.
Best practice: Use fine-thread self-tapping screws for thin materials. Use moderate torque.
Wood Screws
Torque behaviour：Wood screws have coarse, deep threads that cut into the wood fibres as they turn under torque. Wood density heavily influences torque. There is a significant difference between torque requirements for hardwoods (oak, maple, hickory) and softwoods (pine, fir, cedar).
What to watch: Too much torque in wood crushes fibres and strips the hole. The wood around the screw loses its grip, and the screw cannot hold. Under-torque leaves the screw loose—it will work itself out over time under vibration or wood movement.
Best practice: Pre-drill pilot holes in hardwoods to reduce torque requirements. Pilot holes clear out the material so the screw doesn’t have to push it out of the way, reducing friction and torque. Make sure the clutch stops when the drill stalls out, not when the head is flush. Pilot holes are typically optional for softwoods, but are always recommended for thick or dense lumber.
Drywall Screws
Torque behavior: Drywall screws are intended for light duty attachment of gypsum board to wood or steel studs. The bugle head is designed to self-countersink without ripping the paper facing. Torque requirements are relatively low compared to structural fasteners.
What to Watch: Drywall screws are brittle and have no shear strength. They are made of high carbon steel which is hard but not very tough. Over torque will snap the head off or strip the recess, leaving you with a useless screw embedded in the material. If the screw is torqued too little, the head will protrude and it will be difficult to apply joint compound and cause finishing problems.
Best practice: Use a screw gun for drywall that has an adjustable depth setting nose piece. The tool stops feeding when the screw head is at the correct depth – just below the surface of the paper without tearing it. Impact drivers are not use for drywall screws. They snap the heads off with too much torque. Use fine-thread drywall screws (S-type) for wood studs. For steel studs, W-type (coarse thread) drywall screws are used. The torque needed and the holding power of a screw are determined by the type of thread.
Five Torque Myths That Cost Contractors Money.
Myth 1: “Tighter is stronger.”
No. Over-tightening harms fasteners, strips threads and cracks material. A fastener that is tightened to the correct torque is stronger than one that is over-tightened. Hidden damage from over tightening. Does not hold load.
Myth 2: “I can feel the right torque.”
No, you can’t. Human “feel” is not consistent enough for torque control. Different days, different angles, different drivers. The same person will apply different torque each time. The only thing you can count on is a calibrated torque wrench.
Myth 3: “Impact drivers are fine for final torque.”
Fasteners to be tightened to a specified torque should be torqued with a calibrated, manual torque wrench rather than an impact wrench. Impact wrenches are for speed, and not for accuracy.
Myth 4: “Lubrication doesn’t change torque requirements.”
Wrong. Lubrication decreases friction between 20 and 30 %. Applying the same torque to a lubricated fastener as to a dry one results in an over-tightened joint.
Myth 5: “Torque wrenches don’t need calibration.”
Incorrect. Torque wrenches do drift. A torque wrench which is out of calibration is worse than not having one at all, it is giving you false confidence. Calibrate regularly.
How Sinsun Helps You Get Torque Right
We manufacture fasteners that require proper torque to perform as designed. But we do not stop at shipping the product.
For self-drilling, self-tapping, wood, concrete, and drywall screw, we provide torque recommendations based on the specific product, diameter, and application. If you are ordering in bulk, we can include a torque reference card with your shipment—no guessing, no “feel.”
What we offer:
Torque reference values for each screw type and size
Installation best practices for different substrates
Technical support for unusual or demanding applications
Mixed container orders combining multiple screw types in one shipment
For contractors and distributors: If you are training new crews or standardising installation practices across multiple sites, we can provide torque specification sheets tailored to your product mix.
Get the Torque Right, Get the Job Done
Torque is not complicated. It is just precise. A fastener tightened to the correct torque will hold. One that is under-tightened will loosen. One that is over-tightened will fail—maybe immediately, maybe months later, but it will fail.
The difference between a job that stays tight and one that comes back is usually a few Newton-metres and a torque wrench.
Need torque specifications for your next fastener order? Tell us the screw types, diameters, and substrates. We will provide the reference values and installation guidelines.
Contact Sinsun Fasteners for bulk pricing, custom specifications, or technical advice on fastener torque.
Post time: Aug-05-2026