Torque wrenches come in a number of different sizes, and choosing the correct wrench for the job is important. There is no one-size-fits-all solution to properly torquing a fastener, which is why most mechanics have 2 or 3 different sizes in their toolbox.
Common Torque Wrench Sizes
There are five common torque wrench sizes to choose from. The 3/8-inch and 1/2-inch drives are the most common, however, you can also find torque wrenches with 1/4-inch, 3/4-inch, and 1-inch drives. Unless you are working with heavy equipment, you will not have a need for the 3/4-inch or 1-inch drive units.
The 1/4-inch torque wrench is commonly used for working on mopeds, lawnmowers, motorcycles, as well as HVAC, and other smaller fasteners.
The 3/8-inch torque wrench is the second most commonly used wrench and is generally used for most automotive repair work, including spark plugs, alternators, valve covers, oil pans, and most other medium-sized fasteners.
The 1/2-inch torque wrench is the most commonly used wrench and is generally used for larger size fasteners such as lug nuts, suspension bolts, cylinder heads, and other fasteners such as those used to mount the engine to the chassis.
The torque wrench sizes that are 3/4-inch and 1-inch are generally reserved for large vehicles such as tractor-trailers, instruction vehicles, and industrial-grade plumbing.
Which Torque Wrench Size Do I Need?
It is important to choose the right size amongst the variety of torque wrench sizes on the market. Larger drive torque wrenches generally have longer handles which create more torque when tightening a fastener. As a result, you would not want to use a 1/2-inch torque wrench on a small 6 mm fastener because it will easily snap the bolt and half.
The 1/4-inch torque wrench generally provides anywhere from 4 to 21 ft.-lb. of torque which makes it appropriate for smaller fasteners that can be found on valve covers, small engines, as well as bicycles. They provide just enough torque for smaller fasteners, and it is possible to break this smaller drive wrench if it is used on larger fasteners.
The 3/8-inch torque wrench generally provides anywhere from 15 to 75 ft.-lb. of torque which makes it the appropriate choice for most medium-sized fasteners. This drive torque wrench is the most common option for spark plugs, alternators, or any other fastener which would traditionally be tightened using a standard 3/8-inch ratchet.
The 1/2-inch torque wrench generally provides anywhere from 30 to 250 ft.-lb. of torque which makes it perfect for larger fasteners such as lug nuts, spring mounts, shock towers, as well as other suspension and mounting bolts.
The 3/4-inch and 1-inch torque wrenches provide the most amount of torque but are generally not needed by most mechanics and hobbyists.
Click here to read about our article on best digital torque wrench.
What Size Torque Wrench for Car Wheel Lug Nuts?
Choosing the correct size torque wrench for any job is dependent on the size of the actual fastener. When it comes to choosing a torque wrench for car wheel lug nuts, the most important measurement is the size and number of threads on the stud, and not the lug nut itself.
The first step in determining the correct torque wrench to use is to measure the diameter of the fastener. This is difficult to do with a standard tape measure, so it is generally recommended to use calipers for this measurement. The most common diameters studs used on cars are the 5/8-inch, 9/16-inch, 1/2-inch, 7/16-inch, 14 mm, and 12 mm.
Next, you need to count the number of threads per inch or millimeter on the fastener. The higher the thread count, the finer the thread pitch is. To count the thread pitch, simply mark off 1 inch on the SAE fastener or 10 mm on the metric fastener and manually count each individual thread. For the metric fastener, you will need to divide the total number of threads by 10. The most common thread pitches used for SAE lug nuts are 20, 18, and 11, while metric lug nuts are 1.5 and 1.25. As a result, the most common wheel studs are 5/8-11, 5/8-18, 9/16-18, 1/2-20, 7/16-20, 14 mm x 1.50, 12 mm x 1.50, and12 mm x 1.25.
Most 12 mm wheel studs are torqued down to a range between 70 and 80 ft.-lb., whereas 14 mm studs are generally torqued to a range between 85 and 90 ft.-lb. For SAE wheel studs, the 7/16-inch stud is torqued down to a range between 70 and 80 ft.-lb., and the 1/2-inch studs are torqued down to a range between 75 and 85 ft.-lb., while the 9/16-inch studs can be torqued down to a range between 135 and 145 ft.-lb.
Since most automotive lug nuts need to be torqued down to a range between 70 and 145 ft.-lb., the most commonly used torque wrench for the job is a 1/2-inch wrench. While the 3/8-inch torque wrench provides a working range from 15 to 75 ft.-lb. of torque, the 1/2-inch torque wrench provides a working range from 30 to 250 ft.-lb., which makes it the perfect option. The most common lug nut sockets can only be found with a half-inch drive.