Torque Wrench

What it is and how it works

A torque wrench is a calibrated wrench designed to apply a precise amount of twisting force, or torque, to a fastener. Where a regular ratchet simply turns a bolt, a torque wrench measures and controls how tight that bolt gets. This matters because too little torque can let parts loosen, while too much can strip threads, crush gaskets, or even snap the fastener. Most torque wrenches signal that you’ve hit the target setting by a click, a pointer reaching a mark, or an electronic beep and display.

Torque is commonly specified in foot-pounds (ft-lb) or Newton-meters (Nm). Smaller fasteners (electronics, bikes, plumbing bands) may use inch-pounds (in-lb). Always match the unit on the wrench to the unit in the instructions.

Common DIY uses

Automotive and wheels: Tighten wheel lug nuts, engine components, spark plugs, brake calipers, and suspension parts to manufacturer specs.
Bicycles: Stems, handlebars, seatpost clamps, and brake components often specify low torque to protect carbon or aluminum parts.
Small engines and outdoor power equipment: Mower blades, small engine covers, and spark plugs benefit from correct torque.
Anchors and structural hardware: Many wedge anchors, structural bolts, and hardware kits include torque values for safety and performance.
Plumbing bands and couplings: No-hub cast iron couplings and some band clamps specify a torque in inch-pounds to seal correctly without deforming the gasket.
Appliances and fixtures: Certain appliance fasteners and mounting brackets list torque specs to avoid loosening from vibration.

Types of torque wrenches

Click-type: The most common home option. You dial in a torque value; as you pull, the wrench “clicks” and slightly releases when the target is reached. Affordable, accurate (often ±4%), and easy to use.
Beam (deflection) type: A simple beam with a pointer over a scale. As you pull, the pointer moves to show torque. No internal mechanism to wear or lose calibration, but you must watch the scale while pulling.
Digital/electronic: Shows torque on a screen and can beep, vibrate, or light up at the set value. Many can read in ft-lb, Nm, and in-lb and log data. Typically higher cost.
Split-beam: Uses a springless mechanism with a setting dial. Stable long-term, good for frequent use, and doesn’t typically require “backing off” for storage.
Dial type: Highly accurate with an analog dial readout. Common in professional or calibration settings.
Torque screwdriver: A small tool for inch-pound ranges, great for electronics, plumbing bands, and delicate hardware.

Common drive sizes and typical ranges:
- 1/4 in drive: About 20–200 in-lb (2–22 Nm) for small fasteners and bikes.
- 3/8 in drive: About 10–100 ft-lb (13–135 Nm) for general automotive and home tasks.
- 1/2 in drive: About 30–250 ft-lb (40–340 Nm) for lug nuts and larger bolts.

How to choose the right one

Match the range to your jobs: Pick a wrench where your target torque sits near the middle of its scale. For example, lug nuts at 100 ft-lb are well served by a 30–150 ft-lb wrench.
Accuracy and certification: Look for ±4% (or better) accuracy clockwise. Some come with a calibration certificate.
Units and readability: Ensure the scale or display clearly shows ft-lb or Nm as needed.
Drive size and length: Choose 1/4, 3/8, or 1/2 in drive to fit your sockets and intended torque range. A longer wrench reduces effort at higher torques.
Comfort and locking: A comfortable grip and a locking collar prevent accidental changes while working.
Durability and service: Consider brands that offer calibration services and replacement parts.

How to use it correctly

Find the spec: Check the manual or manufacturer instructions for the exact torque and unit, and whether it’s for dry or lubricated threads.
Prepare the fastener: Clean threads. If specified, apply threadlocker or lubricant. Hand-start threads to avoid cross-threading.
Set the torque: Dial in the value and lock the setting. For electronic models, set the target and units.
Use correct sockets: Use quality, six-point sockets that fully engage the fastener. Avoid wobbly adapters that can affect feel.
Grip and pull smoothly: Hold the wrench at the marked grip area. Pull steadily until the click/indicator, then stop. Do not “double-click”; one clean click is your signal.
Patterns matter: For wheels and multi-bolt flanges, snug in a crisscross pattern, then do final torque in the same pattern.
Extensions and crowfoot adapters: Keep a crowfoot at 90 degrees to the wrench to avoid changing the effective length. If you must use it inline, use the manufacturer’s formula or an online calculator to adjust the setting.
After use: For click-type wrenches, turn to the lowest setting (not below the minimum scale). Store clean and dry. Avoid drops and impacts.
Calibration: Have it checked every 12–24 months for frequent use, or after any hard impact. Light DIY users can stretch to a longer interval if accuracy checks compare well.

Mistakes to avoid

Mixing units: Confusing ft-lb with Nm or in-lb leads to large errors. Always confirm the unit.
Using it as a breaker bar: Loosening stuck bolts can damage the mechanism. Use a breaker bar first, then finish with the torque wrench.
Working at the extreme ends: Accuracy is poorer near the bottom and top of the range. Choose a wrench that keeps you in the mid-range.
Fast, jerky pulls: Apply steady pressure for a consistent reading.
Ignoring thread condition: Lubrication, dirt, or threadlocker changes friction and clamping force. Follow the spec’s condition.
Not resetting a click-type: Storing under spring tension can shift calibration over time.

Related terms

Torque: Rotational force that causes a bolt to stretch and clamp parts together.
Foot-pound (ft-lb), Newton-meter (Nm), Inch-pound (in-lb): Common torque units.
Breaker bar: A non-ratcheting lever for loosening tight fasteners.
Torque angle gauge: Measures additional rotation after an initial torque, used on some modern engines.
Torque-to-yield (TTY) bolt: A fastener designed to stretch; usually replaced after removal.
Crowfoot adapter: An open-end attachment that lets you torque flare nuts or hard-to-reach fittings.

Practical examples

Wheel lug nuts: Most passenger cars specify 80–110 ft-lb. Snug in a star pattern, then torque to spec. Recheck after 50–100 miles.
Spark plugs: Commonly 10–25 Nm (7–18 ft-lb). Use a spark plug socket and follow the plug maker’s guidance, especially regarding anti-seize.
Bicycle stem and seatpost: Often 4–6 Nm for stems and 5–7 Nm for seatposts. A small 1/4 in drive or torque screwdriver works well.
Lawn mower blade bolt: Frequently 50–60 ft-lb (check your model). Block the blade safely and torque the bolt; recheck after the first mow.
Wedge anchors: A 3/8 in anchor might call for around 25–30 ft-lb depending on brand. Always follow the anchor manufacturer’s instructions.
No-hub cast iron coupling bands: Commonly 60 in-lb. Use a torque screwdriver or small torque wrench to avoid leaks or gasket damage.

Using a torque wrench builds repeatable, reliable results. It protects parts, improves safety, and makes your repairs and builds last longer.