Torque Range
You measure torque using either the imperial scale in foot-pounds or inch-pounds or the metric scale in newton meters. Most mechanical torque wrenches (the click, beam, and split beam types) include a dual-range scale with foot- or inch-pounds on one side and the corresponding newton meter scale on the other. Digital torque wrenches usually display all three that you toggle through on their LCD screens.
Depending on the wrench, the torque ranges anywhere from 0 to 300 foot-pounds, 0 to 1,000 inch-pounds, or 0 to 400 newton meters. To perform most automotive work, you’ll need a wrench with a range of 10 to 150 foot-pounds or 10 to 200 inch-pounds (and the corresponding newton meter). A smaller range of around 10 to 80 foot-pounds typically suffices for plumbing or HVAC jobs.
Drive Size
A torque wrench’s “drive” protrudes from the wrench’s head and is the square-shaped piece where the socket drive connects. As such, the drive size on the torque wrench must match the socket size. Additionally, the drive size heavily influences the maximum amount of torque a wrench is capable of withstanding and exerting. Larger drives generally correspond to higher torque values.
Handle length also plays a role in the amount of torque a wrench produces, so a larger drive also corresponds to a longer handle. Smaller drive sizes and shorter handle lengths have the lowest torque ranges but are also easier to maneuver in cramped and confined spaces (such as nuts and bolts deep inside your car’s engine bay). Larger drive sizes produce the most torque but are best for tasks where you have plenty of room to operate the longer handle (such as tightening lug nuts).
Torque wrenches are most commonly available with ¼-, ⅜-, and ½-inch drives; the latter two sizes are the most versatile for automotive applications. A ¼-inch drive is commonly found on power tools and works well on small engines (like landscape equipment), as well as plumbing and HVAC components.
Accuracy
You use a torque wrench to ensure that nuts and bolts are within a very specific and narrow range of torque. Because of this, a wrench’s ability to accurately measure the torque you apply is key to avoiding under- or over-tightening.
Torque wrench manufacturers perform calibration tests to measure a wrench’s accuracy. Accuracy ratings average around ±4 percent of the torque value indicated by a wrench’s scale, though higher-end wrenches can be calibrated as precisely as ±2 percent. Many of the high-end models also come with a certificate of calibration to prove that the wrench you purchased was calibrated prior to packaging.
Flexible vs. Fixed Head
A flexible torque wrench head pivots several inches up or down. This gives you some wiggle room when you’re working in tighter spaces where it might be difficult to fit a torque wrench. A fixed head does not pivot at all and is always perpendicular to the handle.
£
